20-letter words starting with a
- asian tiger mosquito — a mosquito, Aedes albopictus, native to Asia, that transmits yellow fever and dengue and possibly West Nile virus. Compare yellow-fever mosquito.
- asleep at the switch — a slender, flexible shoot, rod, etc., used especially in whipping or disciplining.
- assessment procedure — an established method of assessing students or workers
- asset turnover ratio — An asset turnover ratio is a measure of the efficiency of a company, that is calculated by dividing sales for a period by average total assets.
- associated statehood — the semi-independent political status of various former British colonies in the Caribbean from 1967 until each became an independent state in the British Commonwealth, by which Britain retained responsibility for defence and some aspects of foreign affairs. The associated states were Anguilla, Antigua, Dominica, Grenada, St Kitts-Nevis, St Lucia, and St Vincent and the Grenadines
- association football — soccer
- association of stars — a sparsely populated group of between 10 and 1000 young stars of similar spectral type and common origin that are moving too fast to form a permanent, gravitationally bound system.
- astatic galvanometer — a galvanometer that is unaffected by the earth's magnetic field and is used for measuring small currents.
- asymmetrical warfare — warfare between a powerful military force and a weak guerilla force
- at one's convenience — at a time, or in a place or manner, suitable to one
- at one's finger tips — the tip or end of a finger.
- at someone's expense — If you do something at someone's expense, they provide the money for it.
- at someone's service — ready to serve or cooperate with someone
- at the best of times — You say at the best of times when you are making a negative or critical comment to emphasize that it is true even when the circumstances are as favourable as possible.
- at the bottom of sth — If something is at the bottom of a problem or unpleasant situation, it is the real cause of it.
- at the crack of dawn — If you say that someone does something at the crack of dawn, you are emphasizing that they do it very early in the morning.
- at the drop of a hat — If you say that you are ready to do something at the drop of a hat, you mean that you are willing to do it immediately, without hesitating.
- at the eleventh hour — at the last moment; just before it is too late
- at two hours' notice — with notification only two hours in advance
- atmospheric pressure — Atmospheric pressure is the pressure of the atmosphere on the Earth's surface.
- attachment parenting — a style of child rearing aimed at developing a strong emotional bond between the child and primary caregiver. See also attachment (def 3a).
- attacks as a service — (security, legal) A kind of cybercrime as a service in which the service provider performs denial of service attacks on behalf of others for money.
- attendance allowance — (in Britain) a tax-free noncontributory welfare benefit for people over 65 years old who are so severely disabled that they need frequent attention or continual supervision for a period of six months or more
- attic salt (or wit) — graceful, piercing wit
- audio-lingual method — a technique of foreign-language instruction that emphasizes audio-lingual skills over reading and writing and is characterized by extensive use of pattern practice.
- augur ill (or well) — to be a bad (or good) omen
- australian rye grass — a European grass, Lolium multiflorum, naturalized in North America, having flowering spikes and used as a winter turf.
- automobile insurance — Automobile insurance is insurance coverage for cars.
- auxiliary power unit — an additional engine fitted to an aircraft to operate when the main engines are not in use
- axiomatic set theory — (theory) One of several approaches to set theory, consisting of a formal language for talking about sets and a collection of axioms describing how they behave. There are many different axiomatisations for set theory. Each takes a slightly different approach to the problem of finding a theory that captures as much as possible of the intuitive idea of what a set is, while avoiding the paradoxes that result from accepting all of it, the most famous being Russell's paradox. The main source of trouble in naive set theory is the idea that you can specify a set by saying whether each object in the universe is in the "set" or not. Accordingly, the most important differences between different axiomatisations of set theory concern the restrictions they place on this idea (known as "comprehension"). NBG (von Neumann-Bernays-Goedel) set theory sort of allows comprehension for all formulae without restriction, but distinguishes between two kinds of set, so that the sets produced by applying comprehension are only second-class sets. NBG is exactly as powerful as ZF, in the sense that any statement that can be formalised in both theories is a theorem of ZF if and only if it is a theorem of ZFC. MK (Morse-Kelley) set theory is a strengthened version of NBG, with a simpler axiom system. It is strictly stronger than NBG, and it is possible that NBG might be consistent but MK inconsistent. ML ("Modern Logic") is to NF as NBG is to ZF. (Its name derives from the title of the book in which Quine introduced an early, defective, form of it). It is stronger than ZF (it can prove things that ZF can't), but if NF is consistent then ML is too.