slenderize v.

c. 1400, "thin, lean, not fat or fleshy," earlier sclendre (late 14c.), Anglo-French esclendre, from Old French esclendre "thin, slender," which could be from Old Dutch slinder, but according to OED the connection is doubtful.

From 1510s of things, "small in width or diameter as compared to length." By 1520s as "weak, feeble, slight, insignificant, trifling." Related: Slenderly; slenderness.

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.

system for weight loss through diet control, named for William Banting (1797-1878), the English undertaker who invented it, tested it himself, and promoted it in his 1863 booklet "Letter on Corpulence, Addressed to the Public." Although the word is a surname, it was treated as a verbal noun in -ing. ("She is banting"). It consisted of eating lean meats and abstaining from fats, starches, and sugars.