Measure rodent against canine's tail (4)
I believe the answer is:
rate
'measure' is the definition.
(I've seen this before)
'rodent against canine's tail' is the wordplay.
'rodent' becomes 'rat' (rat is a kind of rodent).
'against' is a charade indicator (letters next to each other).
'tail' suggests the final letters.
The last letter of 'canine' is 'e'.
'rat'+'e'='RATE'
(Other definitions for rate that I've seen before include "Degree, proportion, scale" , "Estimate value of - speed" , "Estimate or deserve" , "quality" , "Judge" .)