^_^Please native speakers of English help me with "Bells on bobtail ring"^_^?

Bells on bobtail ring----(1) Making spirits bright What fun it is to ride and sing A sleighing song tonight----(2) Questions: (1) As we know, "bobtail" can mean "a short tail" or "a bobtail horse or a bobtail dog". In this case, what does the "bobtail" in this line... show more Bells on bobtail ring----(1)
Making spirits bright
What fun it is to ride and sing
A sleighing song tonight----(2)

Questions:
(1) As we know, "bobtail" can mean "a short tail" or "a bobtail horse or a bobtail dog". In this case, what does the "bobtail" in this line actually refer to? A tail or a horse?

(2) As we know, a noun sometimes can also be an adjective, say, "table lamp". Then why is it "sleighing song" rather than "sleigh song"?

(3) a sleighing song = a song you sing when you go sleighing?

Please explain in details!

Thank you very much in advance^_^
6 answers 6