Notice which is extraordinarily verbose (7)
I believe the answer is:
observe
'notice' is the definition.
(I know that notice can be written as observe)
'extraordinarily verbose' is the wordplay.
'extraordinarily' indicates anagramming the letters (I've seen this in other clues).
'verbose' with letters rearranged gives 'OBSERVE'.
'which is' acts as a link.
(Other definitions for observe that I've seen before include "See - say" , "taking notice" , "Notice, watch" , "Watch carefully" , "Scrutinise or comply with" .)