Where does “a-” come from?

a- (Sicilian) comes from Latin ad-, from Latin īn-, from Latin în, from Latin en, from Proto-Italic en, from Proto-Indo-European h₁én — in.

a- (Sicilian): crasis of the definite article, colloquial the, colloquial form of u, a, i when followers by a word starting with a vowel

Definitions

crasis of the definite article, colloquial the, colloquial form of u, a, i when followers by a word starting with a vowel

Step	Language	Word	Meaning
1	Latin	ad-	to; usually prefixed to verbs, in which cases it...
2	Latin	īn-	un-, non-, not
3	Latin	în	in, at, on, upon, from (space)
4	Latin	en	lookǃ beholdǃ; reallyǃ?; come onǃ
5	Proto-Italic	en	in
6	Proto-Indo-European	h₁én	in