Stress, tension (6)
I believe the answer is:
strain
I believe this clue is a double definition.
'stress' is the first definition.
(I know that stress can be written as strain)
'tension' is the second definition.
(synonyms)
(Other definitions for strain that I've seen before include "Put through a perforated device to separate" , "Mental tension, stress" , "Pass through a filter" , "Distinct breed (of animal); overexert" , "Pass through a colander" .)