Supply key joke (5)
I believe the answer is:
equip
'supply' is the definition.
(equipping is a kind of supplying)
'key joke' is the wordplay.
'key' becomes 'e' (I've seen this in other clues).
'joke' becomes 'quip' (quipping is a kind of joking).
'e'+'quip'='EQUIP'
(Other definitions for equip that I've seen before include "Supply (with kit)" , "Furnish with requirements" , "Give what's needed" , "Give kit to" , "Provide stuff" .)