Low cry (4)
This clue is a double definition.
'low' is the first definition.
(both can mean to make the noise of a cow)
'cry' is the second definition.
(I know that moo is a type of cry)
(Other definitions for moo that I've seen before include "Cartoon sound of a cow" , "Low (of cattle)" , "Cow's call" , "Irritating woman" , "Bovine low" .)
(Other definitions for moan that I've seen before include "Whinge" , "Complaint" , "Complain; rhymes with money lent" , "Complain, grumble" , "Complain mournfully" .)