Start trip to ignite firework (3,3)
I believe the answer is:
set off
'start' is the definition.
(I know that start can be written as set off)
'trip to ignite firework' is the wordplay.
I cannot really see how this works, but
'to' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for set off that I've seen before include "'Leave on a journey (3,3)'" , "Depart" , "Counterbalance" , "contrast" , "Leave on a journey or put in motion" .)