Fiancée, finally, bound to run off secretly (5)
I believe the answer is:
elope
'run off secretly' is the definition.
(to elope is to run off and get married)
'fiancee finally bound' is the wordplay.
'finally' suggests the final letters.
'bound' becomes 'lope' (to lope is to travel with bounding stride or bound).
The final letter of 'fiancee' is 'e'.
'e'+'lope'='ELOPE'
'to' is the link.
(Other definitions for elope that I've seen before include "Run away secretly to marry" , "Abscond for amorous purposes" , "Run away in secret" , "Run away to get married" , "Do a runner" .)