In'dex1, n.
n.; Eng. pl. IN'DEX-ES; Lat. pl. IN'DI-CĒS. [Lat., from indicere, to proclaim, announce, indicare, to point out, indicate, q. v.] 1. That which points out; that which shows, indicates, or manifests.
Tastes are the indexes of the different qualities of plants. Arbuthnot.
Sense 2. That which guides, points out, or informs, as a pointer or a hand that directs to any thing, as the hour of the day, the road to a place, and the like.
Sense 3. Any table for facilitating reference to topics, names, and the like, in a book; — usually alphabetical in arrangement, and printed at the end of the volume.
Sense 4. (Anat.) The fore finger, or pointing finger.
Sense 5. (Arith. & Alg.) The figure or letter which shows the power or root of a quantity; the exponent. [In this sense the plural is always indices.]
Index error, the error in the reading of a mathematical instrument arising from the zero of the index not being in complete adjustment with that of the limb; a correction to be applied to the instrumental readings equal to the error of the zero-adjustment. — Index finger, the fore finger of the hand: — so called from its use in pointing out. — Index hand, the pointer or hand of a clock, watch, or other registering machine; a hand that points to something. Simmonds. — Index of a logarithm, the integral part of the logarithm, and always one less than the number of integral figures in the given number. It is also called the characteristic. — Index of refraction, or refractive index (Opt.), the number which expresses the ratio of the sine of the angle of incidence to the sine of the angle of refraction. Thus the index of refraction for sulphur is 2, because, when light passes out of air into sulphur, the sine of the angle of incidence is double the sine of the angle of refraction. — Index prohibitory, a catalogue of books which are forbidden by the Roman Catholic church to be read; the index expurgatory, or index expurgatorius, is a catalogue specifying passages in books which are to be expunged or altered. These catalogues are published with additions, from time to time, under the sanction of the pope. Hook.