Surgeon in the slave trade (3)
I believe the answer is:
vet
'surgeon' is the definition.
(I've seen this in other clues)
'in the slave trade' is the wordplay.
'in' indicates the answer is hidden within the clue.
'VET' can be found hidden inside 'slave trade'.
(Other definitions for vet that I've seen before include "'Animal doctor, in short (3)'" , "'Examine this doctor, in short (3)'" , "Examine carefully for suitability" , "Old soldier (inf.)" , "Animal doctor, in brief" .)