Caress a girl on the knee (7)
I believe the answer is:
patella
'knee' is the definition.
(I've seen this before)
'caress a girl on' is the wordplay.
'caress' becomes 'pat' (patting is a kind of caressing).
'a girl' becomes 'ella' (girl's name).
'on' means one lot of letters go next to another.
'pat'+'ella'='PATELLA'
'the' is the link.
(Other definitions for patella that I've seen before include "Knee bone" , "positioned on each knee" , "showing a bit of leg" , "A pallet (anag.)" , "Kneecap (anatomy)" .)