Sorcerer appearing in periodical, American (5)
I believe the answer is:
magus
'sorcerer' is the definition.
(I know that magus is a type of sorcerer)
'periodical american' is the wordplay.
'periodical' becomes 'mag' (abbreviation for magazine).
'american' becomes 'us' (abbreviation for United States).
'mag'+'us'='MAGUS'
'appearing in' acts as a link.
(Other definitions for magus that I've seen before include "astrologer" , "Wizard" , "Priest" , "Balthazar, Gaspar or Melchior individually" , "Guru" .)