Английский Этимологический словарь - tip (3)

- "give a small present of money to," 1610, "to give, hand, pass," originally thieves' cant, perhaps from tip (4) "to tap." The meaning "give a gratuity to" is first attested 1706. The noun in this sense is from 1755; the meaning "piece of confidential information" is from 1845; the verb in this sense is from 1883.