Supply online joke? (5)
I believe the answer is:
'supply' is the definition.
(equipping is a kind of supplying)
'on-line joke?' is the wordplay.
'on-line' becomes 'e' (abbreviation for electronic, e.g. in ecommerce).
'joke?' becomes 'quip' (quipping is a kind of joking).
(Other definitions for equip that I've seen before include "Sally" , "Give everything needed" , "Provide with suitable gear" , "Furnish with supplies" , "Outfit" .)