Definition of since adverb from the Oxford Advanced Learner's Dictionary

      

    since

     adverb
    adverb
    BrE BrE//sɪns//
     
    ; NAmE NAmE//sɪns//
     
    (used with the present perfect or past perfect tense)
     
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  1. 1  from a time in the past until a later past time, or until now He left home two weeks ago and we haven't heard from him since. The original building has long since (= long before now) been demolished.
  2. 2  at a time after a particular time in the past We were divorced two years ago and she has since remarried.
  3. Word Origin late Middle English: contraction of obsolete sithence, or from dialect sin (both from dialect sithen ‘thereupon, afterwards, ever since’).
See the Oxford Advanced American Dictionary entry: since