From The Collaborative International Dictionary of English v.0.48:
Prow \Prow\, a. [Compar. Prower; superl. Prowest.] [OF.
prou, preu, F. preux, fr. L. pro, prod, in prodesse to be
useful. See Pro-, and cf. Prude.]
Valiant; brave; gallant; courageous. [Archaic] --Tennyson.
[1913 Webster]
The prowest knight that ever field did fight.
--Spenser.
[1913 Webster]