Supply teacher's second attempt at humour (5)
I believe the answer is:
equip
'supply' is the definition.
(I know that equip is a more specific form of supply)
'teacher's second attempt at humour' is the wordplay.
'teacher's second' becomes 'e' (und letter of 'teacher').
'attempt at humour' becomes 'quip' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'e'+'quip'='EQUIP'
Can you help me to learn more?
(Other definitions for equip that I've seen before include "Provide with stock" , "Supply (with kit)" , "Sally" , "Provide with kit" , "Give everything needed" .)