syne

[sahyn] /saɪn/
adverb, preposition, conjunction, Scot. and North England
1.
since.
Origin
1300-50; Middle English (north) seine, syn, contraction of sethen since; see sith
British Dictionary definitions for syne

syne1

/səɪn/
adverb, preposition, conjunction
1.
a Scot word for since
Word Origin
C14: probably related to Old English sīth since

syne2

/səɪn/
verb
1.
(transitive) to rinse; wash out
noun
2.
a rinse
Word Origin
C14: of uncertain origin
Word Origin and History for syne
adv.

as in Burns' poem "Auld Lang Syne" (1788) is recorded from c.1300, Scottish form of since (q.v.), without the adverbial genitive inflection.