Small unit that could make mice tremor (10)
I believe the answer is:
micrometre
'small unit' is the definition.
(I've seen this before)
'could make mice tremor' is the wordplay.
'could make' is an anagram indicator.
'mice'+'tremor'='micetremor'
'micetremor' with letters rearranged gives 'MICROMETRE'.
'that' is the link.
(Other definitions for micrometre that I've seen before include "Small unit" , "A short distance" .)