Canine, excessively hot, returns without ring (5)
I believe the answer is:
tooth
'canine' is the definition.
(thesaurus)
'hot returns without ring' is the wordplay.
'returns' says the letters should be written backwards.
'without' is an insertion indicator ('without' can be similar in meaning to 'outside').
'ring' becomes 'ot' (I am not sure about this - if you are sure you should believe this answer much more).
'hot' written backwards gives 'toh'.
'toh' enclosing 'ot' is 'TOOTH'.
'excessively' is the link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for tooth that I've seen before include "Canine, for example" , "Eg, molar" , "Incisor, e.g." , "Fang; cog" , "Taste" .)