What is the Latin word for vainly?

The usual Latin words for “vainly” are frūstrā, nēquīquam, in cassum; also cassus, Catullus. The right choice depends on the sense; see the distinctions below.

English → Latin

“vainly” in Latin

frūstrāin deception, in error; without effect, to no purpose, without cause, uselessly, in vain, for nothing nēquīquamIn vain, vainly, needlessly, uselessly, fruitlessly, pointlessly; to no purpose or effect, without ground or reason in cassumin vain cassushollow, empty, devoid of something; lacking; useless, fruitless, vain, futile Catullusa cognomen; a Latin poet of the late Roman Republic who wrote chiefly in the neoteric style of poetry

Riddle & Arnold A Copious and Critical English–Latin Lexicon, 1864

vainly

In vain, frustra (without effect; i. e., if in any attempt the expected result is not obtained): nequidquam (without carrying one’s point, without any result): incassum (without reaching one’s object or aim: ☞ casse, used by Liv., 24, 16, 10, and cassum, by Sen., Herc., oet., 352, are unusual); also, (The words are found in this connection and order.) frustra ac nequidquam (Catullus, 75, 1); incassum frustraque (Lucr., 5, 1429). ☞ Frustra means “in vain,” with reference to the person who has been disappointed; nequidquam (“in nequidquam, in nihil”) “to no purpose,” refers to the nullity in which the thing has ended. Hence frustra, used adjectively, refers to the person; whereas irritus refers to the thing. Frustra and nequidquam denote merely a failure, without imputing a fault; whereas incassum implies a want of consideration, by which the failure might have been foreseen, Döderlein; but frustra may be used of a thing as employed or done by a person (e.g., frustra telum mittere, Caes.). Labor in vain, labor irritus or labor frustra sumtus (Caes., B.G. 3, 14, 1), or *frustra susceptus; or labor frustra in rem aliquam insumtus. To labor in vain, operam perdere; et operam et oleum perdere (Cic.); oleum et operam perdere (Plaut.): lest my labors should be all in vain, ne et opera et oleum... perierit (Cic.): that attempt was in vain, frustra id inceptum (alicui) fuit (Liv.).

Foolishly, Vid.

Quick answer

What is the Latin word for vainly?: The usual Latin words for “vainly” are frūstrā, nēquīquam, in cassum; also cassus, Catullus. The right choice depends on the sense; see the distinctions below.

Entry from J. E. Riddle & T. K. Arnold, A Copious and Critical English–Latin Lexicon (rev. C. Anthon, New York: Harper, 1864), digitised by Fergus J. P. Walsh, CC BY-SA 4.0; Latin markup adapted by latindictionary.co.