Lock and leave (6)
I believe the answer is:
strand
This clue is a double definition.
'lock' is the first definition.
(I've seen this before)
'leave' is the second definition.
'and' acts as a link.
(Other definitions for strand that I've seen before include "Shore; single fibre" , "Yarn - thread" , "Leave in helpless position" , "Thread; leave in lurch" , "Piece of yarn etc - London street" .)