A small replacement part (4)
I believe the answer is:
scar
'part' is the definition.
The definition and answer can be both to do with contact as well as being verbs in their base form.
Perhaps there's a link between them I don't understand?
'a small replacement' is the wordplay.
'a small' becomes 's' (abbreviation - e.g. clothes size).
'replacement' becomes 'car' (I can't explain this - if you can you should give a lot more credence to this answer).
's'+'car'='SCAR'
Can you help me to learn more?
(Other definitions for scar that I've seen before include "Skin mark; bare crag" , "Identifying mark" , "Permanent mark left by a wound" , "reef" , "Mark left by the healing of injured tissue" .)