Source : Webster's Revised Unabridged Dictionary (1913)

Gander \Gan"der\, n. [AS. gandra, ganra, akin to Prov. G.
   gander, ganter, and E. goose, gannet. See {Goose}.]
   The male of any species of goose.

Source : WordNet®

gander
     n : mature male goose