Lover's knot, we hear (4)
I believe the answer is:
beau
'lover's' is the definition.
(beau is a kind of lover)
'knot we hear' is the wordplay.
'knot' becomes 'bow' (bow is a kind of knot).
'we hear' indicates a 'sounds like' (homophone) clue.
'bow' sounds like 'BEAU'.
(Other definitions for beau that I've seen before include "An old boy friend like Brummel?" , "An old boy friend or dandy" , "Beloved" , "Admirer; fop, dandy" , "One loving" .)