1. from then till now (often prec. by ever): He was elected in 1978 and has been president ever since.
2. between a particular past time and the present; subsequently: She at first refused, but has since consented.
3. ago; before now: long since.
4. continuously from or counting from: It has been warm since noon.
5. between a past time or event and the present: There have been many changes since the war.
6. in the period following the time when: He has written once since he left.
7. continuously from or counting from the time when: He has been busy since he came.
8. because; inasmuch as: Since you're already here, you might as well stay.