Definitely not odd temperature leading to incident (5)
I believe the answer is:
event
'incident' is the definition.
(an incident is an event or happening)
'definitely not odd temperature leading to' is the wordplay.
'definitely not odd temperature' becomes 'even' (I can't justify this - if you can you should give a lot more credence to this answer).
'leading' indicates taking the first letters.
The first letter of 'to' is 't'.
'even'+'t'='EVENT'
Can you help me to learn more?
(Other definitions for event that I've seen before include "Episode" , "Occurren" , "one item in programme" , "tournament" , "Anything which happens" .)