A platform for crazy, heartless ideas (4)
I believe the answer is:
dais
'a platform' is the definition.
(I know that dais is a type of platform)
'crazy heartless ideas' is the wordplay.
'crazy' is an anagram indicator.
'heartless' says to hollow out the word (remove centre letters).
'ideas' with its middle removed is 'idas'.
'idas' is an anagram of 'DAIS'.
'for' is the link.
(Other definitions for dais that I've seen before include "Speaker's raised platform" , "Welshman's" , "Raised floor" , "stand" , "Said to be a low platform" .)