Initially simple lock creating tension (6)
I believe the answer is:
stress
'tension' is the definition.
(synonyms)
'initially simple lock' is the wordplay.
'initially' says to take the initial letters.
'lock' becomes 'tress' (both can mean a piece of hair).
The initial letter of 'simple' is 's'.
's'+'tress'='STRESS'
'creating' is the link.
(Other definitions for stress that I've seen before include "Force" , "what causes tension" , "Emphasis on anxiety?" , "nervous tension" , "why off work?" .)