According to a well-known story, tipping originated in 18th century English coffee houses (or taverns, depending on who's telling it). Supposedly, patrons would put coins in a box marked To Insure Promptness. T.I.P., get it?
Now, nobody has ever found any antique T.I.P. boxes or any mention of them in old books, diaries or letters. But forget that, and forget the fact that "insure" was nearly always spelled "ensure" in the 18th century. Does this story even make sense? We don't tip at the beginning of a meal, to "insure" anything, but at the end, as a reward.
The people we tip--waiters, bartenders, cab drivers, bell hops and so on--all perform personal services that can greatly affect our enjoyment. For instance, we're likely to tip a waiter on the basis of pleasantness, tact, attentiveness to our table, accuracy in conveying our order, helpfulness with the menu and so on.
Promptness probably isn't at the top of the list. In fact, it's something a waiter has little control over--dishes can't be served any faster than they come out of the kitchen. If you want promptness above all, you go to a fast-food place . . . where nobody even expects a tip.
The T.I.P. story sounds plausible to us because words coined on the first letters of a phrase, from "snafu" (situation normal, all fouled up) to "M.A.D.D." (Mothers Against Drunk Driving), are common today. But acronyms, as such words are called, were so rare in earlier times that the word "acronym" itself didn't appear until the 1940s.
So if "tip" doesn't come from T.I.P., where does it come from? It's an 18th century English slang term meaning "to give," which had overtones of friendliness and informality. That's why we not only give tips of money to waiters but tips of inside information to our friends.