Relatively, he takes one to be dirty (5)
I believe the answer is:
uncle
'relatively he' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'one to be dirty' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'un' (I've seen this in other clues) and 'un' is present in the answer.
This may be the basis of clue (or it may be nonsense).
'takes' acts as a link.
Can you help me to learn more?
(Other definitions for uncle that I've seen before include "Family relative" , "Male family member" , "One receiving pawn" , "Male relation; pawnbroker" , "Family relation" .)