Regular temperature, heat may contribute to this (5)
I believe the answer is:
event
'heat may contribute to this' is the definition.
The definition suggests a singular noun which matches the answer.
'regular temperature' is the wordplay.
'regular' becomes 'even' (similar in meaning).
'temperature' becomes 't' (abbreviation).
'even'+'t'='EVENT'
Can you help me to learn more?
(Other definitions for event that I've seen before include "Sporting contest" , "Thing that happens" , "Occurence, happening" , "pole vault maybe" , "400 metres?" .)