It's hot on Haiti, maybe causing stress (10)
I believe the answer is:
intonation
'stress' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Maybe there's an association between them I don't understand?
'it's hot on haiti maybe' is the wordplay.
I cannot quite understand how this works, but
'hot' could be 'in' (both can mean fashionable) and 'in' is found in the answer.
'on' could be 'at' (I've seen this in other clues) and 'at' is present in the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found within the answer.
The remaining letters 'onion' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'causing' is the link.
Can you help me to learn more?
(Other definitions for intonation that I've seen before include "bit of plainsong" , "Rise and fall in voice pitch" , "Feature of speech" .)