Intense, mad look regularly adopted by Olympian (7)
I believe the answer is:
zealous
'intense' is the definition.
(thesaurus)
'mad look regularly adopted by olympian' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'adopted by' indicates putting letters inside (I've seen this in other clues).
'olympian' becomes 'zeus' (Greek god who lived on Mount Olympus).
'mad'+'look'='madlook'
The alternate letters of 'madlook' are 'alo'.
'alo' going into 'zeus' is 'ZEALOUS'.
(Other definitions for zealous that I've seen before include "Avidly enthusiastic" , "Showing great energy and enthusiasm" , "Avid" , "Ardently active" , "Intensely enthusiastic" .)