Since Definition

sĭns

adverb

From then until now or between then and now.

They left town and haven't been here since.

American Heritage

From then until now.

She arrived Tuesday and has been here ever since.

Webster's New World

Before the present time; before now; ago.

They are long since gone.

Webster's New World

At some or any time between then and now; subsequently.

He was ill last week but has since recovered.

Webster's New World

preposition

Continuously from (the time given) until now.

Out walking since one o'clock.

Webster's New World

Intermittently from.

She's been skiing since childhood.

American Heritage

During the period between (the time given) and now; subsequently to.

Many achievements since his election.

Webster's New World

Synonyms:

conjuntion

During the period from the specified time or event until the present.

I haven't seen him since we were in high school.

Webster's New World

Continuously from the time when.

I've been lonely since he left.

Webster's New World

Inasmuch as; because.

Since you are finished, let's go.

Webster's New World

Since you didn't call, we left without you.

Wiktionary

Origin of Since

From Middle English syns, sinnes, contraction of earlier sithens, sithence, from sithen (“after", "since") (+ -s, adverbial genitive suffix), from Old English sīþþan, from the phrase sīþ þǣm (“after/since that (time)"), from sīþ (“since", "after") + þǣm dative singular of þæt. Cognate with Dutch sinds (“since"), German seit (“since"), Danish siden (“since").

From Wiktionary
Middle English sinnes contraction of sithenes sithen since (from Old English siththan) (sīth after) (than) (variant of thām) (dative of thæt that that) -es adv. suff. –s³

From American Heritage Dictionary of the English Language, 5th Edition