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 ]

n. [ Ortho- + Gr. &unr_;, &unr_;, a horn. ] (Zool.) An orthoceras; also, any fossil shell allied to Orthoceras. [ 1913 Webster ]

n. [ Ortho- + Gr. &unr_; to break. ] (Min.) Common or potash feldspar crystallizing in the monoclinic system and having two cleavages at right angles to each other. See Feldspar. [ 1913 Webster ]

a. (Crystallog.) Breaking in directions at right angles to each other; -- said of the monoclinic feldspars. [ 1913 Webster ]

n. [ Ortho- + diagonal. ] (Crystallog.) The diagonal or lateral axis in a monoclinic crystal which is at right angles with the vertical axis. [ 1913 Webster ]

n. [ Ortho- + dome. ] (Crystallog.) See the Note under Dome, 4. [ 1913 Webster ]

n. (Med.) The treatment of the teeth so as to make the teeth align properly within the mouth, usually involving the wearing of braces and sometimes oral surgery. [ PJC ]