I don't know old english but being from Yorkshire I'd take issue with Darowyns meaning of the word 'sithee' or 'sether' not 'sithen' meaning 'suchlike'?, total bollocks! I remember many old relatives of mine using the word (this is people born at the latter end of the 19th century when Yorkshire dialect was still widely spoken) and it was always used in the context of an exclamation as in, 'Now you see here!' ('Nah then sithee!') or "Ow sether!" ...I still use the word myself and it has never, ever been used as a substitute for the word 'suchlike'. I always took it to be a shortened form of "Now you see here!" or "Now see here thee!"
...Just thought I'd chuck in my two pennorth!