Emphasise the origin of safety lock (6)
I believe the answer is:
stress
'emphasise' is the definition.
(I've seen this before)
'the origin of safety lock' is the wordplay.
'the origin of' says to take the initial letters.
'lock' becomes 'tress' (I've seen this before).
The first letter of 'safety' is 's'.
's'+'tress'='STRESS'
(Other definitions for stress that I've seen before include "Put weight on" , "'Strain, tension (6)'" , "Emphasise the pressure" , "possible excuse for sickie?" , "Dwell on" .)