Adept corrected welcomes new stickler (6)
I believe the answer is:
pedant
'stickler' is the definition.
(I've seen this before)
'adept corrected welcomes new' is the wordplay.
'corrected' indicates anagramming the letters.
'welcomes' is an insertion indicator (in sense of 'invites in').
'new' becomes 'n' (abbreviation as in New Testament NT).
'adept' is an anagram of 'pedat'.
'pedat' enclosing 'n' is 'PEDANT'.
(Other definitions for pedant that I've seen before include "Academically fussy person" , "Person who pays undue attention to the rules" , "One excessively concerned with minor detail" , "Know-all who insists on strict observance of rules" , "quibbler" .)