Small, devout wish for one using a jet (7)
I believe the answer is:
sprayer
'one using a jet' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'small devout wish' is the wordplay.
I cannot really understand how this works, but
'small' could be 's' (abbreviation - e.g. clothes size) and 's' is present in the answer.
'wish' could be 'pray' (I've seen this in another clue) and 'pray' is found within the answer.
The remaining letters 'er' 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).
'for' is the link.
Can you help me to learn more?
(Other definitions for sprayer that I've seen before include "type of gun" , "One dispensing deodorant" , "Dispersing agent - aerosol" , "Perhaps Mister" , "Device emitting fine droplets" .)