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' says the answer is hidden in the clue (some parts of the word are used).
'ENORMOUS' is hidden in the letters of 'wren or mouse'.
'could' acts as a link.
(Other definitions for enormous that I've seen before include "Giant" , "Vast" , "Extremely large" , "Immense" , "Massive" .)