Some wren or mouse could be huge (8)
I believe the answer is:
enormous
'be huge' is the definition.
(synonyms)
'some wren or mouse' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'ENORMOUS' is hidden in the letters of 'wren or mouse'.
'could' is the link.
(Other definitions for enormous that I've seen before include "Giant" , "Vast" , "Extremely large" , "Immense" , "Massive" .)