Perhaps measure of gin and it in the end is top (7)
I believe the answer is:
singlet
'is top' is the definition.
(I've seen this before)
'perhaps measure of gin and it in the end' is the wordplay.
I cannot really see how this works, but
'measure' could be 'single' (single is a kind of measure) and 'single' is located in the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found within the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for singlet that I've seen before include "Underwear" , "top gear" , "Sleeveless shirt" , "garment worn by men" , "Sleeveless vest" .)