Old boys smoke out of sight (7)
I believe the answer is:
obscure
'of sight' is the definition.
The answer and definition can be both to do with perception as well as being verbs in their base form.
Maybe you can see an association between them that I can't see?
'old boys smoke' is the wordplay.
'old boys' becomes 'OBs' (OB is short for old boy).
'smoke' becomes 'cure' (as in cured meats).
'obs'+'cure'='OBSCURE'
'out' is the link.
Can you help me to learn more?
(Other definitions for obscure that I've seen before include "Arcane" , "Cloudy or veiled" , "Overshadow or eclipse" , "Dark - secret - inconspicuous" , "Little known - dark" .)