troth
An oath, pledge, plight, or promise.
archaic, countable
By my troth I care not, a man can die but once, we owe God a death, [...]
An oath, pledge, plight, or promise. — A pledge or promise to marry someone.
archaic, countable
His license in the field of time, Unfetter'd by the sense of crime, To whom a conscience never wakes; Nor, what may count itself as blest, The heart that never plighted troth But stagnates in the weeds of sloth;...
...I envy not the beast that takesAn oath, pledge, plight, or promise. — The state of being thus pledged; betrothal, engagement.
archaic, countable
I did, therefore, what an honest man should; restored the maiden her troth, and departed the country, in the service of my king.
Truth; something true.
archaic, countable, uncountable
[John] Martiall, much like to Virgil's Sinon, (of whom he took a precedent, to make an artificial lie,) for three leaves together, in his preface, telleth undoubted trothes; to the end that the falsehoods, which, foolishly, (God wot,) he doth infer, may have the more credit.
Where it comes from
From Middle English troth, trothe, trouthe, trowthe, a variant of treuth, treuthe, treouthe (“allegiance, fidelity, faithfulness, loyalty; oath, pledge, promise; betrothal or marriage vow; betrothal; honour, integrity; holiness, righteousness; confidence, trust; creed, faith; fact, reality, truth”), from Old English trēowþ, trīewþ (“truth, veracity; faith, fidelity; covenant, pledge”), from Proto-Germanic *triwwiþō (“contract; promise”), equivalent to true + -th (abstract nominal suffix). Doublet of truth.
Adapted from the Wiktionary entry troth (CC BY-SA 4.0).