In this context, 'hot' has the opposite meaning of 'cold'.
reverse definition
Frequency:
60
%
The reverse of 'up' is 'down'.
polar opposite
Frequency:
50
%
Their beliefs were polar opposites.
contrary word
Frequency:
45
%
His actions were contrary to his words.
diametrical opposite
Frequency:
35
%
Their viewpoints were diametrically opposite.
Idiomatic Expressions for antonym
Phrase: two sides of the same coin
Meaning: refers to two things that seem different but are actually closely related or connected
Usage: This phrase is often used to highlight the idea that two seemingly opposite or contradictory things are actually part of the same whole.