[1] : The Collaborative International Dictionary of English v.0.48

billy goat \bil"ly goat`\
   a male goat. colloq.
   1913 webster billyo

[2] : WordNet (r) 2.0

billy goat
     n : male goat syn: billy, he-goat
see also:
billy he-goat 

[3] : Moby Thesaurus II by Grady Ward, 1.0

43 moby thesaurus words for "billy goat":
   billy, boar, bubbly-jock, buck, bull, bullock, chanticleer, cock,
   cockerel, doe, doeling, dog, drake, entire, entire horse, gander,
   goat, gobbler, hart, he-goat, kid, mountain goat, nanny,
   nanny goat, peacock, ram, rooster, she-goat, stag, stallion, steer,
   stot, stud, studhorse, tom, tom turkey, tomcat, top cow, top horse,
   tup, turkey gobbler, turkey-cock, wether

Billy Goat >> B Words
Billy Goat, definition of term: Billy Goat
billy+goat_pag1.html

Billy >> B Words
Billy, definition of term: Billy
billy_pag1.html

Goat >> G Words
Goat, definition of term: Goat
goat_pag1.html

Slubbing Billy >> S Words
Slubbing Billy, definition of term: Slubbing Billy
slubbing+billy_pag1.html

Nanny Goat >> N Words
Nanny Goat, definition of term: Nanny Goat
nanny+goat_pag1.html