Webster's Revised Unabridged Dictionary · 1913

Ought

Ought (at) , noun and adverb

See Aught.

Ought , imp., p. p., or auxiliary

[Orig. the preterit of the verb to owe. Old English oughte, aughte, ahte, Anglo-Saxon āhte. r110. See Owe.]

1.
Was or were under obligation to pay; owed. [Obsolete]
This due obedience which they ought to the king. — Tyndale
The love and duty I long have ought you. — Spelman
[He] said... you ought him a thousand pound. — Shakespeare
2.
Owned; possessed. [Obsolete]
The knight the which that castle ought. — Spenser
3.
To be bound in duty or by moral obligation.
We then that are strong ought to bear the infirmities of the weak. — Rom. xv. 1
4.
To be necessary, fit, becoming, or expedient; to behoove; -- in this sense formerly sometimes used impersonally or without a subject expressed.
Well ought us work. — Chaucer
To speak of this as it ought, would ask a volume. — Milton
Ought not Christ to have suffered these things? — Luke xxiv. 26

Ought is now chiefly employed as an auxiliary verb, expressing fitness, expediency, propriety, moral obligation, or the like, in the action or state indicated by the principal verb.