Those illicitly using Tinder? (9)
I believe the answer is:
arsonists
'those illicitly' is the definition.
I can't tell whether this definition defines the answer.
'using tinder?' is the wordplay.
I cannot quite see how this works, but
'using' could be 'on' (someone using drugs is 'on' them) and 'on' is found 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 arsonists that I've seen before include "Criminals" , "people with a burning desire" .)