Over and above what's needed (6)
'over and above what's needed' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for excess that I've seen before include "Over and above what's needed" , "Lack of moderation, in drinking say" , "More than is needed, desired, or required" , "more than enough" , "Plethora" .)
(Other definitions for extra that I've seen before include "One playing a minor part" , "Additional - run - actor - newspaper edition" , "Surplus to requirements" , "Exceptionally" , "Supplemental" .)