So -- losing old lock generates anxiety (6)
I believe the answer is:
stress
'anxiety' is the definition.
(I've seen this before)
'so losing old lock' is the wordplay.
'losing' indicates named letters should be taken away.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'lock' becomes 'tress' (I've seen this before).
'so' with 'o' removed is 's'.
's'+'tress'='STRESS'
'generates' acts as a link.
(Other definitions for stress that I've seen before include "Put weight on" , "'Worry, pressure (6)'" , "possible excuse for sickie?" , "Emotional tension" , "what causes tension" .)