LSJ
Dor. Καφισός, ὁ, Cephisus, name of various rivers, in Phocis, running into Lake Copais, Il. 2.522, Pi. P. 4.46; — fem. λίμνη Κηφισίς Il. 5.709, h.Ap. 280; — Dor. Καφισίς, of the nymph Copais, Pi. P. 12.27; — Adj. Κηφίσιος, α, ον, Dor. Καφίσιος, Id. O. 14.1. at Athens, S. OC 687 (lyr.), etc. in Argolis, etc., Str. 9.3.16, etc. ; — freq. written Κηφισσός in codd., but -σ- in derivs. in Att. Inscrr.
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)