Our son had a semester of college in New Zealand, and he was taught there that the word was an acronym for “To Insure Prompt Service.” There are two problems with that. The first is that the practice of using initials to form acronyms didn’t predate the 20th century, and records of using the word goes back to 1610. The other problem is that “ensure” and not “insure” would be grammatically correct. (I’ve never seen “teps.”) There’s evidence that tipping with money goes back at least the Romans it could just as easily date to the invention of money. Records of employers giving tips to servants dates to the 1700s. Snopes declares that the description of the word as an acronym is false.