troth

[trawth, trohth] /trɔθ, troʊθ/
noun
1.
faithfulness, fidelity, or loyalty:
by my troth.
2.
truth or verity:
in troth.
3.
one's word or promise, especially in engaging oneself to marry.
Origin
1125-75; Middle English trowthe, trouthe, variant of treuthe, Old English trēowth. See truth
Related forms
trothless, adjective
British Dictionary definitions for troth

troth

/trəʊθ/
noun (archaic)
1.
a pledge or oath of fidelity, esp a betrothal
2.
truth (esp in the phrase in troth)
3.
loyalty; fidelity
Word Origin
Old English trēowth; related to Old High German gitriuwida loyalty; see truth
Word Origin and History for troth
n.

late 12c., from a phonetic variant of Old English treowð "faithfulness, truth" (see truth). Restricted to Midlands and Northern England dialect after 16c., and to certain archaic phrases (e.g. plight one's troth). Cf. also betroth.