Demi’s heartless, so cruel, wrongly entraps Douglas finally in this movie (10)
I believe the answer is:
disclosure
'entraps douglas finally in this movie' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'demi's heartless so cruel wrongly' is the wordplay.
'demi's heartless' becomes 'dis' (I can't explain this - if you can you should believe this answer much more).
'wrongly' indicates an anagram.
'so'+'cruel'='socruel'
'socruel' anagrammed gives 'closure'.
'dis'+'closure'='DISCLOSURE'
Can you help me to learn more?
(Other definitions for disclosure that I've seen before include "revealing" , "Publication" , "Laying bare" , "Act of revelation" , "leak" .)