Let everybody cry! (5)
I believe the answer is:
allow
'let' is the definition.
('allow' can be a synonym of 'let')
'everybody cry' is the wordplay.
'everybody' becomes 'all' (I've seen this before).
'cry' becomes 'ow' (I can't explain this - if you can you should give a lot more credence to this answer).
'all'+'ow'='ALLOW'
Can you help me to learn more?
(Other definitions for allow that I've seen before include "Tolerate" , "Give leave to" , "Grant" , "Permit, let happen" , "Permit, consent to" .)