Simple substances that make up the weather (8)
I believe the answer is:
elements
'weather' is the definition.
(I know that elements is a type of weather)
'simple substances that make up the' is the wordplay.
I cannot quite see how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found within the answer.
'substances' could be 'ns' (N is an example) and 'ns' is found within the leftover letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for elements that I've seen before include "Carbon, iron and 8 Across, say" , "Eg, helium and silver" , "Essential parts or the weather" , "eg Fire, air" , "Basic principles of the weather" .)