Dialect causes stress (6)
I believe the answer is:
accent
This clue is a double definition.
'dialect' is the first definition.
(synonyms)
'stress' is the second definition.
(accent can mean to emphasise or stress)
'causes' acts as a link.
(Other definitions for accent that I've seen before include "A localised way of speaking" , "Local way of speaking or enunciation" , "Place stress on, say a syllable" , "Underline" , "Emphasis on syllabus or word" .)