Definition of since conjunction from the Oxford Advanced American Dictionary

     

    since

     conjunction
    conjunction
    NAmE//sɪns//
     
     
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  1. 1 (used with the present perfect, past perfect, or simple present tense in the main clause) from an event in the past until a later past event, or until now Cath hasn't phoned since she went to Berlin. It was the first time I'd had visitors since I'd moved to New Haven. It's twenty years since I've seen her. How long is it since we last went to the theater? She had been worrying ever since the letter arrived.
  2. 2because; as We thought that, since we were in the area, we'd stop by and see them.
See the Oxford Advanced Learner's Dictionary entry: since