Job lot held back voided for a laugh (7)
I believe the answer is:
chortle
'for a laugh' is the definition.
(chortle is a kind of laugh)
'job lot held' is the wordplay.
'job' becomes 'chore' (synonyms).
'lot' becomes 'tl' (I am not sure about this - if you are sure you should believe this answer much more).
'held' means one lot of letters goes inside another.
'chore' going around 'tl' is 'CHORTLE'.
'back voided' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for chortle that I've seen before include "Loud gleeful chuckle" , "Laugh gleefully" , "Chuckle merrily" , "Laugh softly" , "Chuckle gleefully" .)