The particular commercial senses of "make safe against loss by payment of premiums; undertake to ensure against loss, etc." are from mid-17c. (replacing assure in that meaning). Related: Insured; insuring.
Commercial sense of "security against loss or death in exchange for payment" is from 1650s. Assurance was the older word for this specific sense (late 16c.). Compare insure.
Also used with native and imported elements to form verbs from nouns and adjectives, with a sense "put in or on" (encircle), also "cause to be, make into" (endear), and used as an intensive (enclose). Spelling variants in French that were brought over into Middle English account for parallels such as ensure/insure, and most en- words in English had at one time or another a variant in in-, and vice versa.
"give a small present of money to," c. 1600, originally "to give, hand, pass," thieves' cant, perhaps from tip (v.3) "to tap." The meaning "give a gratuity to" is first attested 1706. The noun in this sense is from 1755; the noun meaning "piece of confidential information" is from 1845; and the verb in the sense "give private information to" is from 1883.
The popularity of the tale of the word's supposed origin as an acronym in mid-18th century English taverns seems to be no older than Frederick W. Hackwood's 1909 book "Inns, Ales and Drinking Customs of Old England," where it was said to stand for To insure promptitude (in the form to insure promptness the anecdote is told from 1946). A reviewer of the book in The Athenaeum of Oct. 2, 1909, wrote, "We deprecate the careless repetition of popular etymologies such as the notion that "tip" originated from an abbreviated inscription on a box placed on the sideboard in old coaching-inns, the full meaning of which was "To Insure Promptitude." Also see here.
late 14c., preserven, "keep safe or free from harm," also "act so as to insure that something does not occur," from Anglo-French preservare, Old French preserver, Medieval Latin preservare "keep, preserve," all from Late Latin praeservare "guard beforehand," from Latin prae "before" (see pre-) + servare "to keep safe" (from PIE root *ser- (1) "to protect").
From early 15c. as "maintain, keep in a certain quality, state or condition." Of fruit, etc., "prevent from spoiling by use of preservative substances," 1570s; of organic bodies, "keep in existence or alive," from 1610s. Related: Preserved; preserver; preserving.
