Definitions for a
prefix 1. prefix ā shortened before a double consonant. 2. a negative prefixed to nouns, adjectives; and participles. 3. the augment prefixed to some roots in the Past and Conditional Tenses; e.g. akāsi.
the prep. ā shortened before double cons., as akkosati (ā + kruś), akkhāti (ā + khyā), abbahati (ā + bṛh)
Best to be classed here is the a- we call expletive. It represents a reduction of ā- (mostly before liquids and nasals and with single consonant instead of double). Thus anantaka (for ā-nantaka = nantaka) Vv.80#7; amajjapa (for ā-majjapa = majjapa) Ja.vi.328; amāpaya (for āmāpaya = māpaya) Ja.vi.518; apassato (= passantassa) Ja.vi.552.
(an- before vowels) neg. part. prefixed to 1 nouns and adjectives; 2 verbal forms, used like (1) whether part., ger., grd. or inf.; 3 finite verbal forms. In compound. with words having originally two initial cons. the latter reappear in their assimilated form (e.g. appaṭicchavin). In meaning it equals na-, nir- and vi-. Often we find it opp. to sa-. Verbal negatives which occur in specific verb. function will be enumerated. separately, while examples of neg. forms of (1) & (2) are given under their positive form unless the neg. involves a distinctly new concept, or if its form is likely to lead to confusion or misunderstanding
Concerning the combining & contrasting (orig. neg.) -a-(ā) in redupl. formations like bhavā-bhava see ā4.
Vedic a-, an-; Idg. *n̊, gradation form to *ne (see na2); Gr. ἀ, ἀν-; Lat. *en-, in-; Goth. Ohg. & Ags. un-; Oir. an-, in-
the augment (sign of action in the past), prefixed to the root in pret., aor. & cond.; tenses; often omitted in ordinary prose. See forms under each verb; cp. also ajja Identical with this a- is the a- which functions as base of some pron. forms like ato, attha, asu etc. (q.v.).
Vedic a-; Idg. *e (loc. of pron. stem, cp. ayaṃ; orig. a deictic adv. with specific reference to the past, cp Sk sma); Gr. ἐ-; also in Gr. ἐκεϊ, Lat. equidem, enim.
the sound a (a-kāra) Ja.vi.328, Ja.vi.552; Vv-a.279, Vv-a.307, Vv-a.311.