Bouncy castle collapses, trapping one (7)
I believe the answer is:
elastic
'bouncy' is the definition.
(similar in meaning)
'castle collapses trapping one' is the wordplay.
'collapses' is an anagram indicator.
'trapping' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'castle' is an anagram of 'elastc'.
'elastc' placed around 'i' is 'ELASTIC'.
(Other definitions for elastic that I've seen before include "Stretcher" , "Castile (anag)" , "Able to give a bit" , "Giving" , "It's lace (anag.)" .)