I. noun 1. the first letter of the alphabet. 2. denoting the first in a set of items, categories, sizes, etc. 3. denoting the first of two or more hypothetical people or things • suppose A had killed B.
4. the highest class of academic mark. • a dazzling array of straight A’s.
5. (in the UK) denoting the most important category of road, other than a motorway • the A34
• busy A-roads.
6. denoting the highest-earning socio-economic category for marketing purposes, including top management and senior professional personnel. 7. ( a) —
[Chess] denoting the first file from the left, as viewed from White’s side of the board.
8. (usu. a) — the first constant to appear in an algebraic expression. 9.
[Geology] denoting the uppermost soil horizon, especially the topsoil.
10. the human blood type (in the ABO system) containing the A antigen and lacking the B. 11. (with numeral) denoting a series of international standard paper sizes each twice the area of the next, as A0, A1, A2, A3, A4, etc., A4 being 210 × 297 mm. 12. a shape like that of a capital A[in combination] • an A-shape.
[Music] the sixth note of the diatonic scale of C major. The A above middle C is usually used as the basis for tuning and in modern music has a standard frequency of 440 Hz.
14. a key based on a scale with A as its keynote. II. phrases 1. from A to B from one’s starting point to one’s destination • most road atlases will get you from A to B.
2. from A to Z over the entire range; completely. • make sure you understand the subject from A to Z.
3. plan A one’s original plan or strategy • plan A having gone horribly wrong, Ferguson used the interval to change his formation.
Compare with plan B.