One armed and dangerous person has it in for you, we hear (6)
I believe the answer is:
hitman
'one armed and dangerous' is the definition.
I know nothing about this answer so I can't tell whether this works.
'person has it in for you we hear' is the wordplay.
I cannot really understand how this works, but
'person' could be 'tman' (T-man is an example) and 'tman' is found within the answer.
The remaining letters 'hi' 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).
(Other definitions for hitman that I've seen before include "Assassin" , "offer?" , "Hired gun" , "killer" .)