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Equal; isomeric.

Greek isos, equal.

In meteorology, an isobar (Greek barus, heavy) is a line on a map connecting points having the same barometric pressure; a triangle that is isosceles (Greek skelos, leg) has two sides of equal length; something isomorphic (Greek morphē, form) is similar in form and relations to another; an object or substance that is isotropic (Greek tropos, a turn) has a physical property which has the same value when measured in different directions; isotopes are forms of the same element that contain different numbers of neutrons in their nuclei (Greek topos, place, because the forms occupy the same place in the periodic table of elements).

Its opposite is aniso‑.

In chemistry, iso‑ indicates that a compound is isomeric with another, indicating that they have the same number and kind of atoms but that they are arranged differently in the molecule: isooctane, a liquid hydrocarbon used as a standard in the system of octane numbers; isocyanide, an organic compound containing the group —NC, isomeric with cyanides; isoleucine, an amino acid. See also cis‑ and trans‑.

Isolate and its relatives come instead from Italian isolato, which is derived from Latin insula, island.

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