Rain on the way leads to stress (6)
I believe the answer is:
strain
'to stress' is the definition.
('strain' can be a synonym of 'stress')
'rain on the way leads' is the wordplay.
'on' is a charade indicator (letters next to each other).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'way' becomes 's' (Compass direction - South).
'leads' says to put letters next to each other (some letters go in front of others).
'rain' put after 't' is 'train'.
'train' put after 's' is 'STRAIN'.
(Other definitions for strain that I've seen before include "Pass through a colander" , "Muscle injury, put liquid through sieve" , "Music" , "Filter - intense effort" , "song" .)