{ . [ L. octo eight, Gr. 'oktw`, with a combining form 'okta-. Cf. Eight. ] A combining form meaning eight; as in octodecimal, octolocular. [ 1913 Webster ]

A prefix meaning eight. See Octo-. [ 1913 Webster ]

n. [ Gr. &unr_; with eight strings; 'okta- (for 'oktw` eight) + &unr_; string, chord: cf. F. octacorde. ] (Mus.) An instrument of eight strings; a system of eight tones. [ Also written octochord. ] [ 1913 Webster ]

n. [ Gr. &unr_;, &unr_;, the number eight. ] 1. (Chem.) An atom or radical which has a valence of eight, or is octavalent. [ 1913 Webster ]

2. A group of eight things. [ PJC ]

a. See Octahedral. [ 1913 Webster ]

‖n. [ NL., fr. Gr. &unr_;, neut. of &unr_; of the eighth day. ] (Eccl.) A fast of eight days before a great festival. Shipley. [ 1913 Webster ]

n. [ Gr. &unr_; eight-cornered; 'okta- (for 'oktw` eight) + &unr_; an angle: cf. F. cctogone. ] 1. (Geom.) A plane figure of eight sides and eight angles. [ 1913 Webster ]

2. Any structure (as a fortification) or place with eight sides or angles. [ 1913 Webster ]

Regular octagon, one in which the sides are all equal, and the angles also are all equal. [ 1913 Webster ]

a. Having eight sides and eight angles. [ 1913 Webster ]

a. [ Octa- + Gr. gynh` wife. ] (Bot.) Having eight pistils or styles; octogynous. [ 1913 Webster ]

a. [ See octahedron. ] Having eight faces or sides; of, pertaining to, or formed in, octahedrons; as, octahedral cleavage; an octahedral crystal. [ 1913 Webster ]

octahedral borax (Chem.), borax obtained from a saturated solution in octahedral crystals, which contain five molecules of water of crystallization; distinguished from common or prismatic borax. --
Octahedral iron ore (Min.), magnetite. [ 1913 Webster ]