Call him one if he's taken criminally?
I believe the answer is:
sneak thief
'call him one' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'if he's taken criminally?' is the wordplay.
'criminally?' is an anagram indicator (I've seen 'criminally' mean this (I've seen this in other clues)).
'if'+'hes'+'taken'='ifhestaken'
'ifhestaken' is an anagram of 'SNEAK-THIEF'.
Can you help me to learn more?
(Other definitions for sneak thief that I've seen before include "he's got some hot booty!" , "nicker?" , "Person who steals via an open door or window" , "He pinches" , "Burglar" .)