Ebenfalls keine St
ory, aber die gleiche Vermutung, hat der Online Etymology Dictionary
(wie der Merriam-Webster über das kleine "i" vor "tip" von LEO aus verlinkt:
"give a small present of money to," 1610, "to give, hand, pass," originally 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 meaning "piece of confidential information" is from 1845; the verb in this sense is from 1883; tipster first recorded 1862.
"light, sharp blow or tap," c.1466, possibly from Low Ger. tippen "to poke, touch lightly," related to M.L.G. tip "end, point," and thus connected to tip (n.); or else connected with tap (v.) "to strike lightly." The noun in this sense is attested from 1567.http://www.etymonline.com/index.php?term=tip