Diner with rigour, methodically eating? (7)
I believe the answer is:
gourmet
'diner' is the definition.
(thesaurus)
'with rigour methodically eating?' is the wordplay.
'with' indicates a hidden word.
'GOURMET' is hidden within 'rigour methodically eating'.
(Other definitions for gourmet that I've seen before include "Epicure" , "One has a passion for fine food and wine" , "Knowledgeable eater" , "One devoted to the refined enjoyment of food and drink" , "connoisser of good food" .)