■ 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 ~').