prep., conj., & adv.
--prep. throughout, or at a point in, the period between (a specified time, event, etc.) and the time present or being considered (must have happened since yesterday; has been going on since June; the greatest composer since Beethoven).
--conj.
1. during or in the time after (what have you been doing since we met?; has not spoken since the dog died).
2 for the reason that, because; inasmuch as (since you are drunk I will drive you home).
3 (ellipt.) as being (a more useful, since better designed, tool).
--adv.
1. from that time or event until now or the time being considered (have not seen them since; had been healthy ever since; has since been cut down).
2 ago (happened many years since).
Etymology: ME, reduced form of obs. sithence or f. dial. sin (f. sithen) f. OE siththon