Witness catches scoundrel in stable (6)
I believe the answer is:
secure
'stable' is the definition.
(I've seen this before)
'witness catches scoundrel' is the wordplay.
'witness' becomes 'see' (synonyms).
'catches' indicates putting letters inside.
'scoundrel' becomes 'cur' (I've seen this before).
'see' placed around 'cur' is 'SECURE'.
'in' acts as a link.
(Other definitions for secure that I've seen before include "Safe and unthreatened" , "land" , "Safe and well-protected" , "Firmly fixed or free from uncertainty" , "lock" .)