One could make a fortune with this! (5)
I believe the answer is:
tarot
'make a fortune with this' is the definition.
The definition suggests a singular noun which matches the answer.
'one' is the wordplay.
I cannot quite see how this works, but
'one' could be 'a' (a thing is one thing) and 'a' is located in the answer.
The remaining letters 'trot' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'could' is the link.
Can you help me to learn more?
(Other definitions for tarot that I've seen before include "78-card pack" , "one may have been taken from deck" , "These cards are used to tell fortunes" , "Set of cards used by fortune-tellers" , "Card used for fortunetelling" .)