Vets manage with small underwear (5)
I believe the answer is:
vests
'vets manage with small underwear' is the definition.
I can't tell whether this definition defines the answer.
'vets manage with small' is the wordplay.
'manage with' indicates anagramming the letters (I've seen 'managed' mean this).
'small' becomes 's' (abbreviation - e.g. clothes size).
'vets' with its letters mixed up with 's' gives 'VESTS'.
Can you help me to learn more?
(Another definition for vests that I've seen is " Sleeveless garments".)