Mr Punch's pet jug (4)
I believe the answer is:
toby
'jug' is the definition.
(I've seen this before)
'mr punch's pet' is the wordplay.
I cannot really understand how this works, but
'mr' could be 'oby' and 'oby' is located in the answer.
A single letter 't' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for toby that I've seen before include "dog with frill round neck" , "Kind of jug" , "Mr Punch's dog, beer-jug" , "Belch, perhaps" , "So-called knight" .)