A mammoth beast disposed to stand and moo (8)
I believe the answer is:
mastodon
'a mammoth' is the definition.
(thesaurus)
'beast disposed to stand and moo' is the wordplay.
I cannot really understand how this works, but
'to' is found in the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for mastodon that I've seen before include "Old mammal" , "Extinct mammal like an elephant" , "old jumbo" , "Huge animal" , "Man stood like extinct sort of elephant" .)