Relevant about river being very hot (8)
I believe the answer is:
tropical
'very hot' is the definition.
(in the tropics)
'relevant about river being' is the wordplay.
I cannot quite understand how this works, but
'about' could be 'ca' (abbreviation for 'circa') and 'ca' is found within the answer.
'river' could be 'r' (abbreviation for river) and 'r' is located in the answer.
'being' could be 'pi' (PI is an example) and 'pi' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for tropical that I've seen before include "rainforest areas" , "Hot and humid, as north and south of the equator" , "Hot and humid, near the equator" , "Describes weather that is hot and humid" , "Boiling" .)