immobilize v.

mid-14c., originally of property; by c. 1400 "steadfast, unmovable" (of faith, etc.), from Old French immoble "immovable, fixed, motionless" (13c., Modern French immeuble), from Latin immobilis "immovable" (also, figuratively, "hard-hearted"), from assimilated form of in- "not, opposite of" (see in- (1)) + mobilis (see mobile (adj.)). Related: Immobilism "policy of extreme conservatism" (1853).

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.