Cope shortened to a considerable extent (3)
I believe the answer is:
far
'to a considerable extent' is the definition.
'cope shortened' is the wordplay.
'cope' becomes 'fare' (eg to fare well is to cope well).
'shortened' means to remove the last letter.
'fare' with its last letter removed is 'FAR'.
(Other definitions for far that I've seen before include "Very much" , "At a great distance way" , "A long, long way to go" , "Remote" , "Distant" .)