A hole with a guinea pig round it (6)
I believe the answer is:
cavity
'a hole' is the definition.
(I know that cavity is a type of hole)
'guinea pig round it' is the wordplay.
'guinea pig' becomes 'cavy' (I've seen this in another clue).
'round' indicates putting letters inside.
'cavy' placed around 'it' is 'CAVITY'.
'with a' is the link.
(Other definitions for cavity that I've seen before include "A hole could mean work for the dentist" , "Hole, crater" , "Destination for a filling!" , "Hole, gap" , "Internal void" .)