This measure is a little one (3)
I believe the answer is:
tot
This clue is a double definition.
'this measure' is the first definition.
(I have seen 'Measure of spirits' mean 'tot' so perhaps 'measure' could also mean 'tot')
'little one' is the second definition.
(thesaurus)
'is a' is the link.
(Other definitions for tot that I've seen before include "Add up, aggregate" , "quick drink" , "Small measure for a small child" , "two fingers, perhaps" , "finger, possibly" .)