Low bar ultimately fell (4)
I believe the answer is:
moor
'fell' is the definition.
(both can mean an expanse of wild land)
'low bar ultimately' is the wordplay.
'low' becomes 'moo' (both can mean to make the noise of a cow).
'ultimately' suggests the final letters.
The final letter of 'bar' is 'r'.
'moo'+'r'='MOOR'
(Other definitions for moor that I've seen before include "African - wasteland" , "Secure boat to fixed object" , "Anchor" , "Heather-covered tract" , "Arab" .)