The Collaborative International Dictionary of English v.0.48:

Navew \Na"vew\, n. [OE. navel, naveau, a dim. fr. L. napus
   navew. Cf. Napiform.] (Bot.)
   A kind of small turnip, a variety of Brassica campestris.
   See Brassica. [Written also naphew.]
   [1913 Webster]