Design safety test with uncertainty (5)
I believe the answer is:
motif
'design' is the definition.
(motif is a kind of design)
'safety test with uncertainty' is the wordplay.
'safety test' becomes 'MOT' (MOT test for a vehicle).
'with' is a charade indicator (letters next to each other).
'uncertainty' becomes 'if' (if can mean a condition or uncertainty).
'mot'+'if'='MOTIF'
(Other definitions for motif that I've seen before include "Recurrent theme as in musical work" , "Theme, perhaps musical" , "Distinctive theme in art" , "Characteristic theme" , "Concept" .)