Unworthy (3)
I believe the answer is:
low
'unworthy' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for low that I've seen before include "Deep sound made by cattle" , "Make a bovine sound" , "Depressed; near the ground" , "SECOND PART OF 14" , "Unimportant sort of owl" .)