Bird stuck in the mud (3)
I believe the answer is:
emu
'bird' is the definition.
(emu is a type of bird)
'stuck in the mud' is the wordplay.
'stuck in' indicates a hidden word.
'EMU' is hidden within 'the mud'.
(Other definitions for emu that I've seen before include "Big bird" , "Parky's nemesis" , "Long-necked bird" , "Australian bird related to the ostrich" , "Aussie runner" .)