21-letter words containing o, s, i
- registration document — a document giving identification details of a motor vehicle, including its manufacturer, date of registration, engine and chassis numbers, and owner's name
- relaxation oscillator — a nonsinusoidal oscillator, the timing of which is controlled by the charge and discharge time constants of resistance and capacitance components
- repatriation expenses — Repatriation expenses are the costs involved in transporting a claimant or their body back to their own country after they have been injured or killed in a foreign country.
- resident commissioner — a representative from a dependency, as Guam or Puerto Rico, who is entitled to speak, but not to vote, in the U.S. House of Representatives.
- residual unemployment — the unemployment that remains in periods of full employment, as a result of those mentally, physically, or emotionally unfit to work
- reverse polish syntax — postfix notation
- revillagigedo islands — an uninhabited island group belonging to Mexico, in the Pacific Ocean, SSW of the Baja California peninsula: Socorro is the largest island. 320 sq. mi. (830 sq. km).
- ring-around-the-rosey — a children's game in which the players sing while going around in a circle and squat when the lyrics “all fall down” are sung.
- rocky mountain locust — a migratory locust, Melanoplus spretus, that occurs in North America, especially the Great Plains, where swarms cause great damage to crops and other vegetation.
- rocky mountain oyster — mountain oyster.
- roll with the punches — a thrusting blow, especially with the fist.
- roll-on-roll-off ship — a cargo ship or ferry designed so that vehicles can be driven straight on and straight off
- rolling in the aisles — (of an audience) overcome with laughter
- roodepoort-maraisburg — a city in S Transvaal, in the NE Republic of South Africa.
- rub someone's nose in — to keep reminding someone of something unpleasant, as a mistake made
- rutherford scattering — the scattering of an alpha particle through a large angle with respect to the original direction of motion of the particle, caused by an atom (Rutherford atom) with most of the mass and all of the positive electric charge concentrated at a center or nucleus.
- s-k reduction machine — An abstract machine defined by Professor David Turner to evaluate combinator expressions represented as binary graphs. Named after the two basic combinators, S and K.
- safe in the knowledge — If you do something safe in the knowledge that something else is the case, you do the first thing confidently because you are sure of the second thing.
- saint anthony's cross — tau cross.
- saint elias mountains — a mountain range between SE Alaska and the SW Yukon, Canada. Highest peak: Mount Logan, 5959 m (19 550 ft)
- saint-maur-des-fosses — a town in N central France, near Paris, on the Marne River.
- salam-weinberg theory — the electroweak theory.
- sales finance company — a finance company that purchases, at a discount, installment contracts from dealers or that finances retail sales.
- sampling distribution — the distribution of a statistic based on all possible random samples that can be drawn from a given population.
- san gabriel mountains — a mountain range in S California, N of Los Angeles. Highest peak, San Antonio Peak, 10,080 feet (3072 meters).
- san gorgonio mountain — a mountain in S California: highest peak in the San Bernardino Mountains. 11,502 feet (3506 meters).
- sanitation department — the department of local government responsible for collecting and disposing of refuse
- sao jose do rio preto — a city in SE Brazil, NW of São Paulo.
- sao tome and principe — Democratic Republic of, a republic in W Africa, comprising the islands of São Tomé and Príncipe, in the Gulf of Guinea, N of the equator: a former overseas province of Portugal; gained independence in 1975. 372 sq. mi. (964 sq. km). Capital: São Tomé.
- saponification number — the number of milligrams of potassium hydroxide required to saponify one gram of a given ester, especially a glyceride.
- satisficing behaviour — the form of behaviour demonstrated by firms who seek satisfactory profits and satisfactory growth rather than maximum profits
- saving your reverence — a form of apology for using an obscene or taboo expression
- scalar multiplication — an operation used in the definition of a vector space in which the product of a scalar and a vector is a vector, the operation is distributive over the addition of both scalars and vectors, and is associative with multiplication of scalars
- scalar triple product — the volume of the parallelepiped defined by three given vectors, u, v, and w, usually represented as u·v 1 (v×w), [ uvw ], or (uvw), where × denotes a cross product and · denotes an inner product.
- schema definition set — (SDS) Something in Portable Common Tool Environment.
- schlieren photography — a type of photography which records schlieren
- scholastic philosophy — the system of philosophy, theology, and teaching that dominated medieval western Europe and was based on the writings of the Church Fathers and (from the 12th century) Aristotle, the Greek philosopher (384–322 bc)
- school of the soldier — an institution where instruction is given, especially to persons under college age: The children are at school.
- school superintendent — an official whose job is to oversee school administration within a district
- schoolgirl complexion — a smooth, clear complexion, such as schoolgirls are considered to have
- science correspondent — a newspaper or television journalist who specializes in reporting on new discoveries in science
- scintillation counter — a device for detecting and measuring radioactivity, having a crystal scintillator, a photoelectric cell sensitive to the light from scintillations, and an amplifier.
- scorched earth policy — a military practice of devastating the property and agriculture of an area before abandoning it to an advancing enemy.
- scorched-earth policy — a military practice of devastating the property and agriculture of an area before abandoning it to an advancing enemy.
- seating accommodation — the provision of seats for people in a room, building, etc
- secondary containment — Secondary containment is a system for dealing with hazardous spills.
- secure hash algorithm —
- self-characterization — portrayal; description: the actor's characterization of a politician.
- sentential connective — any of several words or their equivalent symbols used in logical formulas to connect propositions, as “or,” “not,” “and,” “if and only if.”.
- sequoia national park — a national park in central California: giant sequoia trees. 604 sq. mi. (1565 sq. km).