arcus (noun M) : (the orthography, arquus (cf. arquatus), is freq. in MSS., like quum for cum, quur for cur, etc.; cf. Freund ad Cic. Mil. p. 31 sq. Thus Charis. p. 92 P. upon Cic. N. D. 3, 20, 51, reads arcuis; Prisc. p. 712 P. arci; and Non. p. 425, 5, upon Lucr. 6, 526, arqui; but the distinction which the latter gram. points out (arcus suspensus fornix appellatur; arquus non nisi qui in caelo apparet, quam Irim poëtae dixerunt) does not seem to be well founded.
* Abl. plur. never found; acc. to the gram., Don. p. 1751,Diom. p. 285, Prisc. p. 779, Rhem. Palaem. p. 1371 P. al., it was arcubus; so Vulg. 2 Esdr. 4, 13; cf. Rudd. I. p. 104, n. 48.—Gen. sing. arqui, Lucr. 6, 526 Lachm., and Cic. N. D. 3, 20, 51 B. and K.—Dat. arcu, Sil. 4, 18.—Nom. plur. ARCVVS, Corp. Inscr. V. 85; Inscr. Henz. 5313: arci, Varr. ap. Non. p. 77, 12.—Acc. ARCOS, Corp. Inscr. II. 3420.—Fem., Enn. ap. Prisc. p. 712 P.; cf. id. 658 P.; and Serv. ad Verg. 6, 610, says that Catull. and others used it as fem.; v. Neue, Formenl. I. p. 679) [cf. Sanscr. arālas = bent, the bent arm, aratnis = Gr. ὠλένη; Lat. ulna; Germ. Elbogen; Engl. elbow. Curt.], prop., something bent; hence
* A bow (syn. cornu).
* For shooting: intendit crinitus Apollo Arcum auratum, Enn. ap. Cic. Ac. 2, 28, 89 (Trag. v. 54 Müll.): arcus intentus in aliquem,Cic. Sest. 7: haec cernens arcum intendebat Apollo Desuper,Verg. A. 8, 704; 9, 665; so Vulg. Psa. 10, 3; 36, 14: arcum tendere,ib. 3 Reg. 22, 34; ib. 4 Reg. 9, 24: adductus,Verg. A. 5, 507: remissus,Hor. C. 3, 27, 67: arcum dirigere in aliquem,Pers. 3, 60: quom arcum et pharetram mi et sagittas sumpsero,Plaut. Trin. 3, 2, 98; so, arcum suscitare,Vulg. Hab. 3, 9 et saep.
* Transf.
* A bow or arch in building, a vault, arch, triumphal arch, etc.: efficiens humilem lapidum compagibus arcum,Ov. M. 3, 30; 3, 160; Juv. 3, 11; Suet. Ner. 25: marmoreus arcus,id. Claud. 1; so id. ib. 11; id. Dom. 13; cf. Plin. Pan. 59, 2 Schwarz.
* Poet. or in post-Aug. prose, any thing arched or curved like a bow; of the breaking of waves: niger arcus aquarum,Ov. M. 11, 568.—Of the windings of a serpent: immensos saltu sinuatur in arcus,Ov. M. 3, 42.—Of a curve in flight: dea se paribus per caelum sustulit alis Ingentemque fugā secuit sub nubibus arcum,Verg. A. 5, 658.—Of the curving or bendings of a bay: sinus curvos falcatus in arcus,Ov. M. 11, 229 (cf.: inque sinus scindit sese unda reductos,Verg. A. 1, 161).— Of a harbor: Portus ab Euroo fluctu curvatus in arcum,Verg. A. 3, 533.—Of boughs of trees, Verg. G. 2, 26 et saep.—Of the back of a chair, Tac. A. 15, 57.
* The mathematical arc, Sen. Q. N. 1, 10; Col. 5, 2, 9.—Hence, of the five parallel circles of the globe which bound the zones (or perhaps rather, the zones themselves): via quinque per arcus,Ov. M. 2, 129.

s. TLL