Large adhesive label covers disciplinarian (8)
I believe the answer is:
stickler
'disciplinarian' is the definition.
(I know that stickler is a type of disciplinarian)
'large adhesive label covers' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'adhesive label' becomes 'sticker' (I've seen this before).
'covers' indicates putting letters inside.
'l' inserted within 'sticker' is 'STICKLER'.
(Other definitions for stickler that I've seen before include "Someone fastidious" , "Person who insists on something, say punctuality - sounds adhesive" , "Fusspot" , "One insisting on correctness" , "Punctilious, insistent person" .)