Bird or mouse? (7)
I believe the answer is:
chicken
I believe this is a double definition.
'bird' is the first definition.
(I know that chicken is a type of domestic fowl)
'mouse?' is the second definition.
(thesaurus)
'or' acts as a link.
(Other definitions for chicken that I've seen before include "Bird, coward (colloq.)" , "Prov. cowardly bird" , "Proverbial road-crosser" , "Cowardly (colloq.)" , "Yellow-bellied" .)