Why is the ninth month called September?
"to slope, overturn," c.1300, possibly from Scandinavian, or a special use of tip (n.). Intransitive sense of "fall over" is recorded from 1520s. Related: Tipped; tipping. Tipping point attested by 1972.
"give a small present of money to," c.1600, "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. For urban legendary origin as an acronym, see here.
"end, point, top," early 13c., from Middle Low German or Middle Dutch tip "utmost point, extremity, tip" (cf. German zipfel, a diminutive formation); perhaps cognate with Old English tæppa "stopper" (see tap (n.)), from Proto-Germanic *tupp- "upper extremity." Tip-top is from 1702.
: our tip to him would be to behave (1845+)verb
(also tip off) To give useful information or advice, esp advance information that gives an advantage of some sort: The room clerk tipped him/ Who tipped Larkin off? (1749+, variant 1891+)
[origin uncertain; perhaps fr the notion of tipping, that is, tilting something in someone's direction]
A revealing, esp a warning; a particularly useful clue: the tip-off on what's ahead (1901+)