Ex-GI (3)
I believe the answer is:
vet
'ex-gi' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for vet that I've seen before include "Experienced" , "'Examine this doctor, in short (3)'" , "A small animal doctor" , "Examine carefully - might one help a lame duck?" , "'Animal doctor, in short (3)'" .)