Tiresome foreign diet followed by ordinary American (7)
I believe the answer is:
tedious
'tiresome' is the definition.
('tedious' can be a synonym of 'tiresome')
'foreign diet followed by ordinary american' is the wordplay.
'foreign' indicates anagramming the letters (foreign order of the letters).
'followed by' says to put letters next to each other.
'ordinary' becomes 'o' (abbreviation e.g. O-Levels).
'american' becomes 'us'.
'diet' with letters rearranged gives 'tedi'.
'tedi'+'o'+'us'='TEDIOUS'
(Other definitions for tedious that I've seen before include "awfully boring" , "Tiresome, boring" , "Wearisome, boring" , "Outside (anag.)" , "drab" .)