Fanatical former lover getting married in plane? (7)
I believe the answer is:
extreme
'fanatical' is the definition.
(I've seen this in another clue)
'former lover getting married in plane?' is the wordplay.
'former lover' becomes 'ex' (an ex-lover).
'getting' says to put letters next to each other.
'married' becomes 'm'.
'in' is an insertion indicator.
'plane?' becomes 'tree' (plane tree is a type of tree).
'm' placed inside 'tree' is 'treme'.
'ex'+'treme'='EXTREME'
(Other definitions for extreme that I've seen before include "lacking moderation" , "Farthest limit" , "Very intense - way-out" , "Utmost; excessive" , "Draconian" .)