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n. (Zool.) Any one of numerous small two-winged flies of the family Ortalidae. The larvae of many of these flies live in fruit; those of others produce galls on various plants. [ 1913 Webster ]

n. (Zool.) A brachiopod shell of the genus Orthis, and allied genera, of the family Orthidae. [ 1913 Webster ]

‖prop. n. [ NL., fr. Gr. 'orqo`s straight. ] (Zool.) An extinct genus of Brachiopoda, abundant in the Paleozoic rocks. [ 1913 Webster ]

n. [ Gr. 'orqo`s straight. ] (Min.) A variety of allanite occurring in slender prismatic crystals. [ 1913 Webster ]

pos>pref. [ Gr. 'orqo`s straight; akin to Skr. ūrdhva upright, v&rsdot_;dh to grow, to cause to grow. ] [ 1913 Webster ]

1. A combining form signifying straight, right, upright, correct, regular; as, orthodromy, orthodiagonal, orthodox, orthographic. [ 1913 Webster ]

2. (Chem.) A combining form (also used adjectively), designating: (a) (Inorganic Chem.) The one of several acids of the same element (as the phosphoric acids), which actually occurs with the greatest number of hydroxyl groups; as, orthophosphoric acid. Cf. Normal. (b) (Organic Chem.) Connection with, or affinity to, one variety of isomerism, characteristic of the benzene compounds; -- contrasted with meta- or para-; as, the ortho position; hence, designating any substance showing such isomerism; as, an ortho compound. [ 1913 Webster ]

☞ In the graphic representation of the benzene nucleus (see Benzene nucleus, under Benzene), provisionally adopted, any substance exhibiting double substitution in adjacent and contiguous carbon atoms, as 1 & 2, 3 & 4, 4 & 5, etc., is designated by ortho-; as, orthoxylene; any substance exhibiting substitution of two carbon atoms with one intervening, as 1 & 3, 2 & 4, 3 & 5, 4 & 6, etc., by meta-; as, resorcin or metaxylene; any substance exhibiting substitution in opposite parts, as 1 & 4, 2 & 5, 3 & 6, by para-; as, hydroquinone or paraxylene. [ 1913 Webster ]

a. [ Ortho- + carbonic. ] (Chem.) Designating a complex ether, C.(OC2H5)4, which is obtained as a liquid of a pleasant ethereal odor by means of chlorpicrin, and is believed to be a derivative of the hypothetical normal carbonic acid, C.(OH)4. [ 1913 Webster ]

n. [ Ortho- + center. ] (Geom.) That point in which the three perpendiculars let fall from the angles of a triangle upon the opposite sides, or the sides produced, mutually intersect. [ 1913 Webster ]

‖n. [ NL., fr. Gr. 'orqo`s straight + ke`ras a horn. ] (Paleon.) An extinct genus of Paleozoic Cephalopoda, having a long, straight, conical shell. The interior is divided into numerous chambers by transverse septa. [ 1913 Webster ]