A sweet one can be both sound and hot! (5)
I believe the answer is:
tooth
'a sweet' is the definition.
(thesaurus)
'sound and hot' is the wordplay.
'sound' becomes 'toot' (toot is a kind of sound**).
'and' means one lot of letters go next to another.
'hot' becomes 'h'.
'toot'+'h'='TOOTH'
'one can be both' is the link.
I am not very happy about this link. Some or all of 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 "Jag on the edge of a saw" , "for drilling and extraction" , "In which the old are long" , "Canine, for example" , "Chopper" .)