Some nerve tissue from old hand (3)
I believe the answer is:
vet
'old hand' is the definition.
(thesaurus)
'some nerve tissue from' is the wordplay.
'from' says the answer is hidden in the clue.
'VET' can be found hidden inside 'some nerve tissue'.
(Other definitions for vet that I've seen before include "animal doctor to > investigate" , "Examine carefully for suitability" , "Animal doctor, in brief" , "Old soldier (inf.)" , "Dog doc?" .)