Sic | Webster's Dictionary of the English Language

sic
sīc (old form sīce, Plaut. Rud. 2, 4, 12; also seic, C. I. L. 818), adv. [for si - ce; si, locat. ...

A New Latin Dictionary by Charlton T. Lewis Ph.D. and Charles Short, LL. D.
sic
sīc adv. for the old sīce; sī (locat. of pron. stem sa-)+ce.—Referring to something done...

An Elementary Latin Dictionary