Keeps on dropping end of it round — round head of cattle, perhaps (5)
I believe the answer is:
lasso
'it round round head of cattle perhaps' is the definition.
The definition suggests a singular noun which matches the answer.
'keeps on dropping end of' is the wordplay.
I cannot quite see how this works, but
'of' could be 'o' and 'o' is found within the answer.
The remaining letters 'lass' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for lasso that I've seen before include "Cowcatcher" , "A cowboy's looped lariat" , "Cattle-catching rope" , "Belgian composer" , "Rancher's rope" .)