Lewis & Short

1. irrĭtus (inr-), a, um, adj. [2. inratus], invalid.

  1. I. Lit.
    1. A. Undecided, unfixed, void, of no effect: quod modo erat ratum, irritum est, Ter. Phorm, 4, 7, 58: testamentum irritum facere, Cic. Phil. 2, 42, 109: testamentum pro irrito habere, Suet. Tib. 51; Gai. Inst. 2, 146 sq.; Paul. Sent. 3, 5, 14: injurias rescindere et irritas facere, Cic. Verr. 2, 2, 26, § 63: quaeque augur injusta, nefasta, vitiosa, dira, defixerit, inrita infectaque sunto, id. Leg. 2, 8, 21: omnia ab iis acta, Vell. 2, 43, 1: pacta, Sil. 6, 696: Tiberii voluntas, Suet. Calig. 14: somnia, of no significance, id. Aug. 91: Remus aves irritas habuit, Gell. 13, 14.
    2. B. Vain, useless, without effect, ineffectual: ingrata atque irrita esse omnia intellego, Plaut. As. 1, 2, 10: inceptum, Liv. 29, 35; 24, 19: dona, Verg. G. 4, 519: tela, id. A. 2, 459: moenia, Ov. M. 12, 587: labor anni, id. ib. 1, 273; Quint. 12, 1, 13: verba, Ov. R. Am. 286: tua dicta factaque, Cat. 30, 10: spes, Liv. 22, 20; Stat. Th. 10, 45: oblivio, Liv. 28, 29: lingua (Cassandrae), Prop. 3, 13 (4, 12), 66: remedium, Tac. H. 4, 81: preces, Plin. Pan. 26: ova, fruitless, infertile, Plin. 10, 58, 79, § 160.
  2. II. Transf., of persons, that does or undertakes a thing in vain, to no purpose, without effect.
          1. (α) With gen.: irritus legationis, Tac. H. 4, 32: consilii, Vell. 2, 63, 2: propositi, Val. Max. 4, 3, 3 ext.: spei, vainly hoping, Curt. 6, 5, 31: incepti, Sil. 7, 131.
          2. (β) Absol.: variis assultibus irritus urget, Verg. A. 5, 442: venit et e templis irrita turba domum, without a response, Tib. 2, 3, 22: irriti legati remittuntur, Tac. A. 15, 25: domum irritus rediit, Sen. Ben. 6, 11: discedere irritum putebat, Curt. 4, 4, 2: irritus qui habebatur, laudabatur, good for nothing, Cat. ap. Gell. 11, 2, 2.
            Subst.: irrĭtum, i, n., nothingness, vanity, worthlessness: spes ad irritum redacta, Liv. 28, 31: spes ad irritum cadens, id. 2, 6: victoria ad inritum revolvebatur, Tac. H. 3, 26: cecidisse in inritum labores, id. ib. 3, 53 fin.: irrita dicere, useless words, Ov. M. 11, 40.
            Adv.: irrĭtē, in vain, Cassiod. Var. 1, 4; 12, 2.