troth 
(trôth, trŏth, trōth)
(trôth, trŏth, trōth)n.
1.
a. Betrothal.
b. One's pledged fidelity.
2. Good faith; fidelity.
tr.v. trothed, troth·ing, troths
To pledge or betroth.
[Middle English trouthe, trothe, variant of treuthe, from Old English trēowth, truth; see deru- in the Appendix of Indo-European roots.]