Pressure someone initially put on lock (6)
I believe the answer is:
stress
'pressure' is the definition.
(I've seen this in another clue)
'someone initially put on lock' is the wordplay.
'initially' indicates taking the first letters.
'put on' means one lot of letters go next to another.
'lock' becomes 'tress' (both can mean a piece of hair).
The initial letter of 'someone' is 's'.
's'+'tress'='STRESS'
(Other definitions for stress that I've seen before include "why off work?" , "Physical or mental over-exertion" , "Lay emphasis on - it's a strain" , "result of being overworked" , "Highlight" .)