a (2)EnglishOxford New American Dictionarya2 ▸ abbreviation 1 (in travel timetables) arrives: Penzance a 0915. 2 [in combination] (in units of measurement) atto- (10−18). 3 British (with reference to sporting fixtures) away: March 15 Sheffield United (a). 4 (used before a date) before: a1200. [from Latin ante.] ▸ symbol (a) Physics acceleration.