though Look up though at Dictionary.com
c.1200, from O.E. žeah, and in part from O.N. žo "though," both from P.Gmc. *thaukh (cf. Goth. žauh, O.Fris. thach, M.Du., Du. doch, O.H.G. doh, Ger. doch), from PIE demonstrative pronoun *to- (see that). The evolution of the terminal sound did not follow laugh, tough, etc., though a tendency to end the word in "f" existed c.1300-1750 and persists in dialects.