Litter or mess (7)
I believe the answer is:
clutter
I believe this clue is a double definition.
'litter' is the first definition.
(thesaurus)
'mess' is the second definition.
(clutter is mess or disorganisation)
(Other definitions for clutter that I've seen before include "Confused mess" , "Clog up" , "Untidy mess" , "Confusion" , "Disorderly accumulation" .)