Elaborated about the big end (8)
I believe the answer is:
enlarged
'elaborated' is the definition.
(I've seen this before)
'about the big end' is the wordplay.
'about' indicates putting letters inside.
'the big' becomes 'large' (I've seen this before).
'large' inserted inside 'end' is 'ENLARGED'.
(Other definitions for enlarged that I've seen before include "Magnified" , "Made bigger like photo" , "puffed out?" , "Blew up" , "Increased, augmented" .)