Set off from Thailand by ship (7)
I believe the answer is:
trigger
'set off' is the definition.
(synonyms)
'thailand by ship' is the wordplay.
I cannot really understand how this works, but
'thailand' could be 't' (abbreviation on car registration plates) and 't' is located in the answer.
The remaining letters 'rigger' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'from' acts as a link.
Can you help me to learn more?
(Other definitions for trigger that I've seen before include "Releasing device" , "prompt" , "One pulled to fire" , "Cause (device) to operate" , "Equine film star" .)