Flimsy item falling short (4)
I believe the answer is:
thin
'flimsy' is the definition.
(similar in meaning)
'item falling short' is the wordplay.
'item' becomes 'thing' (both can mean an object).
'falling short' means to remove the last letter.
'thing' with its last letter taken away is 'THIN'.
(Other definitions for thin that I've seen before include "Unconvincing" , "as 7 [LOAF] may be sliced" , "Scrawny" , "Lean; narrow" , "Implausible" .)