Severity or strictness (6)
I believe the answer is:
rigour
This clue is a double definition.
'severity' is the first definition.
(I know that severity can be written as rigour)
'strictness' is the second definition.
(I know that rigour is a type of strictness)
(Other definitions for rigour that I've seen before include "Trial" , "Severity or stringency" , "Stiffness or strictness" , "Quality of being extremely thorough and careful" , "Severity, harshness" .)