Maiden in Exeter might be exceptional (7)
I believe the answer is:
extreme
'exceptional' is the definition.
(synonyms)
'maiden in exeter might be' is the wordplay.
'maiden' becomes 'm' (cricket abbreviation).
'in' is an insertion indicator.
'might be' indicates anagramming the letters.
'exeter' is an anagram of 'extree'.
'm' going into 'extree' is 'EXTREME'.
(Other definitions for extreme that I've seen before include "Of the greatest intensity" , "Exceptional - radical" , "stiff" , "over the top" , "Farthest limit" .)