One holding a person’s hat by peak (6)
I believe the answer is:
captor
'one holding a person's' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'hat by peak' is the wordplay.
'hat' becomes 'cap' (cap is a type of hat).
'by' says to put letters next to each other.
'peak' becomes 'tor' (a tor is a rocky peak).
'cap'+'tor'='CAPTOR'
Can you help me to learn more?
(Other definitions for captor that I've seen before include "He catches someone" , "One who takes a prisoner" , "Holder of a prisoner" , "He takes someone prisoner" , "One imprisoning another" .)