Sweet, warm hearted, silly Gus (5)
I believe the answer is:
sugar
'sweet' is the definition.
(thesaurus)
'warm hearted silly gus' is the wordplay.
I cannot quite see how this works, but
an anagram of 'gus' is 'sug' which is within the answer.
The remaining letters 'ar' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for sugar that I've seen before include "See 11" , "Term of affection" , "Damn" , "Basic sweetener" , "Sweeten" .)