Emphasis, strain (6)
I believe the answer is:
stress
This clue is a double definition.
'emphasis' is the first definition.
(I know that stress is a type of emphasis)
'strain' is the second definition.
(I know that stress is a type of strain)
(Other definitions for stress that I've seen before include "Force" , "Emphasise the pressure" , "'Worry, pressure (6)'" , "Emphasis on anxiety?" , "Emphasise the strain" .)