a reduced form of the Old English preposition on, meaning “on,” “in,” “into,” “to,” “toward,” preserved before a noun in a prepositional phrase, forming a predicate adjective or an adverbial element (afoot; abed; ashore; aside; away), or before an adjective (afar; aloud; alow), as a moribund prefix with a verb (acknowledge), and in archaic and dialectal use before a present participle in -ing (set the bells aringing); and added to a verb stem with the force of a present participle (ablaze; agape; aglow; astride; and originally, awry).

Origin of a-

Middle English, late Old English; cf. a2, nowadays

Definition for a- (2 of 7)


a reduced form of the Old English preposition of: akin; afresh; anew.

Origin of a-

Middle English; see a3

Definition for a- (3 of 7)


an old point-action prefix, not referring to an act as a whole, but only to the beginning or end: She arose (rose up). They abided by their beliefs (remained faithful to the end).

Origin of a-

Middle English; Old English a- (unstressed), ǣ-, ā-, ō- (stressed; see abb, woof1, oakum), rarely or- (see ordeal) ≪ Germanic *uz- < unstressed Indo-European *uss- < *ud-s, akin to out; in some cases confused with a-4, as in abridge

Definition for a- (4 of 7)


variant of ab- before p and v: aperient; avert.

Origin of a-

Middle English < Latin ā-, a- (variant of ab- ab-); in some words < French a- < Latin ab-, as in abridge

Definition for a- (5 of 7)


variant of ad-, used: (1) before sc, sp, st (ascend) and (2) in words of French derivation (often with the sense of increase, addition): amass.

Origin of a-

Middle English, in some words < Middle French a- < Latin ad- prefix or ad preposition (see ad-), as in abut; in others < Latin a- (variant of ad- ad-), as in ascend

Definition for a- (6 of 7)


variant of an-1 before a consonant, meaning “not,” “without”: amoral; atonal; achromatic.

Definition for a- (7 of 7)


atomic (used in combination): A-bomb; A-plant.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

British Dictionary definitions for a- (1 of 2)


before a vowel an-


not; without; opposite toatonal; asocial

Word Origin for a-

from Greek a-, an- not, without

British Dictionary definitions for a- (2 of 2)



on; in; towardsafoot; abed; aground; aback
literary, or archaic (used before a present participle) in the act or process ofcome a-running; go a-hunting
in the condition or state ofafloat; alive; asleep
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Medical definitions for a-



Without; not:acellular.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Scientific definitions for a-


A prefix meaning “without” or “not” when forming an adjective (such as amorphous, without form, or atypical, not typical), and “absence of” when forming a noun (such as arrhythmia, absence of rhythm). Before a vowel or h it becomes an- (as in anhydrous, anoxia).
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.