Valley dropping away, largely empty, first of all (4)
I believe the answer is:
dale
'valley' is the definition.
(I know that valley can be written as dale)
'dropping away largely empty first of all' is the wordplay.
'first of all' suggests taking the first letters.
The first letters of 'dropping away largely empty' is 'DALE'.
(Other definitions for dale that I've seen before include "Lead into poetic valley" , "Up hill and down . . . ." , "Valley, particularly in Northern England" , "See 8" , "An English valley" .)