A 1 (a wun). A registry mark given by underwriters (as at Lloyd’s) to ships in first-class condition. Inferior grades are indicated by A 2 and A 3. A 1 is also applied colloquially to other things to imply superiority; prime; first-class; first-rate.

A B C
A B C" (a be se").
1. The first three letters of the alphabet, used for the whole alphabet.
2. A primer for teaching the alphabet and first elements of reading. [Obs.]
3. The simplest rudiments of any subject; as the A B C of finance. A B C book, a primer. Shak.

A cappella
A cap•pel"la . [It. See Chapel.] (Mus.) (a) In church or chapel style; — said of compositions sung in the old church style, without instrumental accompaniment; as a mass a capella, i. e., a mass purely vocal. (b) A time indication, equivalent to alla breve.

A fortiori
A for•ti•o"ri . [L.] (Logic & Math.) With stronger reason.

A mensa et thoro
A men"sa et tho"ro . [L., from board and bed.] (Law) A kind of divorce which does not dissolve the marriage bond, but merely authorizes a separate life of the husband and wife. Abbott.

A posteriori
A• pos•te•ri•o"ri . [L. a ( ab) + posterior latter.]
1. (Logic) Characterizing that kind of reasoning which derives propositions from the observation of facts, or by generalizations from facts arrives at principles and definitions, or infers causes from effects. This is the reverse of a priori reasoning.
2. (Philos.) Applied to knowledge which is based upon or derived from facts through induction or experiment; inductive or empirical. { A•pos´til, A•pos´tille } n. [F. apostille. See Postil.] A marginal note on a letter or other paper; an annotation. Motley.

A priori
A• pri•o"ri . [L. a ( ab) + prior former.]
1. (Logic) Characterizing that kind of reasoning which deduces consequences from definitions formed, or principles assumed, or which infers effects from causes previously known; deductive or deductively. The reverse of a posteriori.
3. (Philos.) Applied to knowledge and conceptions assumed, or presupposed, as prior to experience, in order to make experience rational or possible.
"A priori that is form these necessities of the mind or forms of thinking which, though first revealed to us by experience must yet have preëxisted in order to make experience possible." - Coleridge.