The Collaborative International Dictionary of English v.0.48:

Portgreve \Port"greve`\, Portgrave \Port"grave`\, [AS.
   portger[=e]fa; port a harbor + ger[=e]fa a reeve or sheriff.
   See Reeve a steward, and cf. Portreeve.]
   In old English law, the chief magistrate of a port or
   maritime town.; a portreeve. [Obs.] --Fabyan.
   [1913 Webster]