In full gear he commonly told a joke (8)
I believe the answer is:
equipped
'in full gear he' is the definition.
The definition suggests a singular noun but the answer is not.
'commonly told a joke' is the wordplay.
'commonly' becomes 'e' (I can't justify this - if you can you should give a lot more credence to this answer).
'told a joke' becomes 'quipped' (quipping is a kind of telling a joke).
'e'+'quipped'='EQUIPPED'
Can you help me to learn more?
(Other definitions for equipped that I've seen before include "Fitted out with whatever's necessary" , "Having the right tools for the job" , "Provided" , "Furnished" , "Fitted out with what's necessary" .)