Barker's doctor (may also treat Tom) (3)
I believe the answer is:
vet
I believe this is a triple definition!
'barker's doctor' is the first definition.
'vet' can be an answer for 'doctor' (vet is a kind of doctor). I am unsure of the 'barker's' bit.
'may' is a link.
'also' is the second definition.
(thesaurus)
'treat tom' is the third definition.
'vet' can be an answer for 'treat' (vetting is a kind of treating). I am unsure of the 'tom' bit.
Can you help me to learn more?
(Other definitions for vet that I've seen before include "Experienced" , "Animal doctor, in brief" , "A diminutive animal doctor" , "Scrutinise" , "Old soldier (inf.)" .)