¦ preposition in the intervening period between (the time mentioned) and the time under consideration.
¦ conjunction
1. during or in the time after.
2. for the reason that; because.
¦ adverb
1. from the time mentioned until the present or the time under consideration.
2. ago.
Origin
ME: contr. of obs. sithence, or from dialect sin (both from dialect sithen 'thereupon, afterwards, ever since').