Ox-like, bigheaded and sheepish (6)
I believe the answer is:
bovine
'ox-like' is the definition.
(I've seen this before)
'bigheaded and sheepish' is the wordplay.
'bigheaded' becomes 'b' (this could be a standard abbreviation I've not previously seen).
'and' means one lot of letters go next to another.
'sheepish' becomes 'ovine' (I've seen this before).
'b'+'ovine'='BOVINE'
Can you help me to learn more?
(Other definitions for bovine that I've seen before include "To do with cows, dull and stupid" , "Ox-like" , "Like or to do with cows" , "Cowlike" , "(Like a) yak, for example" .)