18-letter words containing a, p, r, i, o
- protocol data unit — (PDU) A packet of data passed across a network. The term implies a specific layer of the OSI seven layer model and a specific protocol.
- provably difficult — The set or property of problems for which it can be proven that no polynomial-time algorithm exists, only exponential-time algorithms.
- provascular tissue — procambium.
- provincial council — (formerly) a council administering any of the New Zealand provinces
- provision merchant — a person or company in the business of retailing food and other provisions
- przewalski's horse — a wild horse, Equus caballus przevalskii, chiefly of Mongolia and Sinkiang, characterized by light yellow coloring and a stiff, upright black mane with no forelock: the only remaining breed of wild horse, it is now endangered and chiefly maintained in zoos.
- pseudo-anarchistic — a person who advocates or believes in anarchy or anarchism.
- psychotherapeutics — psychotherapy.
- public corporation — a corporation, owned and operated by a government, established for the administration of certain public programs.
- pulmonary embolism — the blockage of a pulmonary artery, often by a blood clot, that stops the flow of blood to the lungs and which can result in death if untreated
- pulmonic airstream — a current of lung air set in motion by the respiratory muscles in the production of speech.
- purchasing officer — the member of staff in an organization who is responsible for buying goods or products
- pyromucic aldehyde — furfural.
- pyrosulphuric acid — a fuming liquid acid made by adding sulphur trioxide to concentrated sulphuric acid. Formula: H2S2O7
- qattara depression — a desert basin in the Libyan Desert, in NW Egypt: lowest point is 435 feet (133 meters) below sea level. 6950 sq. mi. (18,000 sq. km).
- quartz-iodine lamp — a type of tungsten-halogen lamp containing small amounts of iodine and having a quartz envelope, operating at high temperature and producing an intense light for use in car headlamps, etc
- rabbit-proof fence — a fence through which rabbits are unable to pass
- radiation exposure — exposure to radiant energy or to the particles emitted in the transfer of radiant energy, esp the particles and gamma rays emitted in nuclear decay; exposure to radioactive substances
- radiation pressure — the pressure exerted on a surface by electromagnetic radiation or by sound waves.
- radical expression — an expression in which radical signs appear.
- rapid eye movement — rapidly shifting, continuous movements of the eyes beneath closed lids during the stage of sleep characterized by dreaming.
- rational operation — any of the mathematical operations of addition, subtraction, multiplication, and division.
- reactive component — the component in an alternating-current circuit that does not contribute power because it is 90° out of phase with the voltage or current.
- real-time computer — a computer that can process data or information almost immediately
- recess appointment — a person appointed to an office by the President of the United States without approval from the Senate because the Senate is in recess
- reciprocating pump — A reciprocating pump is a pump which uses a backward and forward movement to move a fluid.
- recovery operation — the process of locating and retrieving bodies, esp following an explosion or natural disaster
- registered company — a company which has officially registered its business
- registration plate — a plate mounted on the front and back of a motor vehicle bearing the registration number
- regular expression — 1. (text, operating system) (regexp, RE) One of the wild card patterns used by Perl and other languages, following Unix utilities such as grep, sed, and awk and editors such as vi and Emacs. Regular expressions use conventions similar to but more elaborate than those described under glob. A regular expression is a sequence of characters with the following meanings (in Perl, other flavours vary): An ordinary character (not one of the special characters discussed below) matches that character. A backslash (\) followed by any special character matches the special character itself. The special characters are: "." matches any character except newline; "RE*" (where RE is any regular expression and the "*" is called the "Kleene star") matches zero or more occurrences of RE. If there is any choice, the longest leftmost matching string is chosen. "^" at the beginning of an RE matches the start of a line and "$" at the end of an RE matches the end of a line. (RE) matches whatever RE matches and \N, where N is a digit, matches whatever was matched by the RE between the Nth "(" and its corresponding ")" earlier in the same RE. Many flavours use \(RE\) instead of just (RE). The concatenation of REs is a RE that matches the concatenation of the strings matched by each RE. RE1 | RE2 matches whatever RE1 or RE2 matches. \< matches the beginning of a word and \> matches the end of a word. Many flavours use "\b" instead as the special character for "word boundary". RE{M} matches M occurences of RE. RE{M,} matches M or more occurences of RE. RE{M,N} matches between M and N occurences. Other flavours use RE\{M\} etc. Perl provides several "quote-like" operators for writing REs, including the common // form and less common ??. A comprehensive survey of regexp flavours is found in Friedl 1997 (see below). 2. Any description of a pattern composed from combinations of symbols and the three operators: Concatenation - pattern A concatenated with B matches a match for A followed by a match for B. Or - pattern A-or-B matches either a match for A or a match for B. Closure - zero or more matches for a pattern. The earliest form of regular expressions (and the term itself) were invented by mathematician Stephen Cole Kleene in the mid-1950s, as a notation to easily manipulate "regular sets", formal descriptions of the behaviour of finite state machines, in regular algebra.
- reinforced plastic — plastic with fibrous matter, such as carbon fibre, embedded in it to confer additional strength
- report an accident — If you report an accident, you inform an insurer or the police or other authorities that an accident has occurred.
- reprocessing plant — a plant where materials are treated in order to make them reusable
- respiratory arrest — cessation of breathing
- respiratory system — the system by which oxygen is taken into the body and an exchange of oxygen and carbon dioxide takes place; in mammals the system includes the nasal passages, pharynx, trachea, bronchi, and lungs.
- resurrection plant — a desert plant, Selaginella lepidophylla, occurring from Texas to South America, having stems that curl inward when dry.
- rhodes scholarship — one of a number of scholarships at Oxford University, established by the will of Cecil Rhodes, for selected students (Rhodes scholars) from the British Commonwealth and the United States.
- scholarship holder — a person who, because of academic merit, receives financial aid for their studies
- scissors-and-paste — designating or of a piece of writing that has been assembled from a variety of sources rather than by original research, often in a hasty or uninspired way
- seafloor spreading — a process in which new ocean floor is created as molten material from the earth's mantle rises in margins between plates or ridges and spreads out.
- seasonal promotion — Seasonal promotions are items marketed to customers at the appropriate time of year, such as coats in the winter and bathing suits in the summer.
- secondary syphilis — the second stage of syphilis, characterized by eruptions of the skin and mucous membrane.
- self-preoccupation — the state of being preoccupied.
- separation anxiety — the normal fear and apprehension expressed by infants when removed from their mothers or approached by strangers.
- september holidays — a period of time in September when people do not have to go to school, college or work
- septic sore throat — an acute, toxic, streptococcus infection of the throat producing fever, tonsillitis, and other serious effects.
- shipping container — a large, strong container, usually of metal, used to store goods in during shipment
- shunting operation — an operation in which rail coaches are manoeuvred
- simple enumeration — a procedure for arriving at empirical generalizations by haphazard accumulation of positive instances.
- slow-motion replay — a showing again in slow motion of a sequence of action, esp of part of a sporting contest immediately after it happens