It's hot, it's cold, they say (6)
I believe the answer is:
chilli
'it's hot' is the definition.
I can't judge whether this defines the answer.
'cold they say' is the wordplay.
'cold' becomes 'chilly' (I've seen this before).
'they say' indicates a 'sounds like' (homophone) clue.
'chilly' is a homophone of 'CHILLI'.
'it's' is the link.
Can you help me to learn more?
(Other definitions for chilli that I've seen before include "Pungent pod" , "Hot one in dish maybe" , "Hot stuff (though sounding otherwise)" , "'Red, green or yellow pepper (6)'" , "Hot red pepper used as seasoning" .)