"variety of magnetite characterized by its power of attracting iron and steel," mid-15c. (earlier magnes, late 14c.), from Old French magnete "magnetite, magnet, lodestone," and directly from Latin magnetum (nominative magnes) "lodestone," from Greek ho Magnes lithos "the Magnesian stone," from Magnesia (see magnesia), region in Thessaly where magnetized ore was obtained. Figurative sense of "something which attracts" is from 1650s.
It has spread from Latin to most Western European languages (German and Danish magnet, Dutch magneet, Italian, Spanish, Portuguese magnete), but it was superseded in French by aimant (from Latin adamas; see adamant (n.)). Italian calamita "magnet" (13c.), French calamite (by 16c., said to be from Italian), Spanish caramida (15c., probably from Italian) apparently is from Latin calamus "reed, stalk or straw of wheat" (see shawm) "the needle being inserted in a stalk or piece of cork so as to float on water" [Donkin]. Chick magnet attested from 1989.
word-forming element used to make verbs, Middle English -isen, from Old French -iser/-izer, from Late Latin -izare, from Greek -izein, a verb-forming element denoting the doing of the noun or adjective to which it is attached.
The variation of -ize and -ise began in Old French and Middle English, perhaps aided by a few words (such as surprise, see below) where the ending is French or Latin, not Greek. With the classical revival, English partially reverted to the correct Greek -z- spelling from late 16c. But the 1694 edition of the authoritative French Academy dictionary standardized the spellings as -s-, which influenced English.
In Britain, despite the opposition to it (at least formerly) of OED, Encyclopaedia Britannica, the Times of London, and Fowler, -ise remains dominant. Fowler thinks this is to avoid the difficulty of remembering the short list of common words not from Greek which must be spelled with an -s- (such as advertise, devise, surprise). American English has always favored -ize. The spelling variation involves about 200 English verbs.