The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

gander
    n 1: mature male goose

Moby Thesaurus II by Grady Ward, 1.0:

76 Moby Thesaurus words for "gander":
   Bantam, banty, barn-door fowl, barnyard fowl, biddy, billy,
   billy goat, boar, broiler, brooder, broody hen, bubbly-jock, buck,
   bull, bullock, capon, chanticleer, chick, chickabiddy, chicken,
   chicky, cock, cockerel, dog, domestic fowl, drake, duck, duckling,
   dunghill fowl, entire, entire horse, fowl, fryer, game fowl,
   glance, glimpse, gobbler, goose, gosling, guinea cock, guinea fowl,
   guinea hen, hart, he-goat, hen, hen turkey, partlet, peacock, peek,
   peep, poulard, poult, poultry, pullet, ram, roaster, rooster,
   setting hen, spring chicken, stag, stallion, steer,
   stewing chicken, stot, stud, studhorse, tom, tom turkey, tomcat,
   top cow, top horse, tup, turkey, turkey gobbler, turkey-cock,
   wether