n. In Roman antiquity, a conical column or post, or, usually, a group of three such posts, at each end of the spina of a circus, serving to mark the place of turning; a turning-post.n. A prefix in words of Greek origin or formation, meaning ‘among, between, with, after, beyond, over,’ etc., often denoting change or transformation (like L. trans-), in which denotation it is much used in the formation of new terms in science. :In inorganic chem., among the different types of periodic, phosphoric, arsenious, arsenic, boracic, and silicic: acids, a prefix used in the name of that which contains the least proportion of hydrogen.As a prefix to the names of benzene derivations, it signifies that atoms or radicals substituting two, three, or four of the hydrogen atoms of benzene have the positions (if all six hydrogen atoms of the original benzene be numbered consecutively from 1 to 6) 1 and 3, 1, 2, and 4, or 1, 2, 3, and 5, respectively. This arrangement is spoken of as asymmetric. In geology, it is used to denote change, transformation, or metamorphism, but differently in different instances. In one case the rock-name to which it is prefixed accords with the present character of the rock, and the prefix meta- indicates that it has been developed by processes of metamorphism: as, meta-diorite, a diorite which has resulted from metamorphism, possibly of a gabbro. In another case the rock name describes the rock as it was before metamorphism: as, meta-diabase, for an altered diabase.
