Thoughts cast aside (5)
I believe the answer is:
ideas
'thoughts' is the definition.
(I know this)
'cast aside' is the wordplay.
'cast' indicates anagramming the letters (letters are dispersed or cast around).
'aside' anagrammed gives 'IDEAS'.
(Other definitions for ideas that I've seen before include "Notions, concepts" , "Thoughts, creative perhaps" , "Brain waves" , "Thoughts, perceptions" , "Thoughts or opinions" .)