Small mouselike mammal (5)
I believe the answer is:
shrew
'small mouselike mammal' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for shrew that I've seen before include "Small insectivore" , "Insectivorous mammal" , "Small mouselike animal" , "Shakespeare: 'The Taming of the ....'" , "Scold; insectivore" .)