You leave a tip to insure promptness, and the word literally says so: T.I.P. People love telling waiters this, usually while not tipping enough. The story goes that English coffee houses had a box on the counter marked TIP, and you dropped a coin in to get served faster. Neat. Memorable. The kind of thing that sounds like it belongs in a museum.
The word predates the supposed acronym by a long way, and it would be 'ensure' promptness, not 'insure', which is a separate verb about insurance policies. 'Tip' meaning to hand over a small sum shows up as thieves' and tavern slang in the 1600s, part of a family of 'tip' words meaning to pass something along quietly. There is no coffee-house box with TIP painted on it in any contemporary record. Like 'posh' and 'golf', this is a backronym, a backwards-built acronym glued onto an existing word because the story is satisfying to retell. If a word is older than the office memo, it was not born as an acronym. Tipping is old. Acronyms are not.
Reception
- Online Etymology Dictionary: tipREFERENCE
- Wikipedia: Gratuity (etymology)REFERENCE