Sound of an ungraceful landing (4)
I believe the answer is:
thud
'sound of an ungraceful landing' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for thud that I've seen before include "Dull heavy noise" , "Dull sound of something hitting the ground" , "Clunk" , "Noise of dull impact" , "Clonk" .)