Plain and pistachio nuts ordered by editor (15)
I believe the answer is:
unsophisticated
'plain' is the definition.
(thesaurus)
'pistachio nuts ordered by editor' is the wordplay.
'ordered' indicates anagramming the letters.
'by' is a charade indicator (letters next to each other).
'editor' becomes 'ed'.
'pistachio'+'nuts'='pistachionuts'
'pistachionuts' is an anagram of 'unsophisticat'.
'unsophisticat'+'ed'='UNSOPHISTICATED'
'and' acts as a link.
(Other definitions for unsophisticated that I've seen before include "green" , "Simple" , "straightforward" , "crude" , "Lacking experience" .)