1610s, "a rope for hoisting," probably a blend or confusion of pendant in the nautical sense of "suspended rope" and pennon "long, narrow flag." Use for "flag on a warship" is by 1690s; as "flag long in the fly as compared with its hoist," 1815. The meaning "flag symbolizing a sports championship" (especially baseball) is from 1880; as a synonym for "championship" it is attested by 1915.
c. 1300, "inscription, heading," from Old French title "title or chapter of a book; position; legal permit" (12c., Modern French titre, by dissimilation), and in part from Old English titul, both from Latin titulus "inscription, label, ticket, placard, heading; honorable appellation, title of honor," of unknown origin. Meaning "name of a book, play, etc." first recorded mid-14c. The sense of "name showing a person's rank" in English is first attested 1580s. Sports championship sense attested from 1913 (originally in lawn tennis), hence titlist (1913). A title role in theater is one which gives its name to the play.
The "hand motion" meaning is recorded from 1680s; meaning "undulating line" is recorded from 1660s. Of people in masses, first recorded 1852; in physics, from 1832. Sense in heat wave is from 1843. The crowd stunt in stadiums is attested under this name from 1984, the thing itself said to have been done first Oct. 15, 1981, at the Yankees-A's AL championship series game in the Oakland Coliseum; soon picked up and popularized at University of Washington. To make waves "cause trouble" is attested from 1962.
Old English belt "belt; girdle; broad, flat strip or strap of material used to encircle the waist," from Proto-Germanic *baltjaz (source also of Old High German balz, Old Norse balti, Swedish bälte), an early Germanic borrowing from Latin balteus "girdle, sword belt," said by Varro to be an Etruscan word.
Transferred sense of "broad stripe encircling something with its ends joined" is from 1660s; that of "broad strip or tract" of any sort, without notion of encircling (as in Bible belt is by 1808). As a mark of rank or distinction, mid-14c.; references to boxing championship belts date from 1812. Mechanical sense is from 1795. Below the belt "unfair" (1889) is from pugilism. To get something under (one's) belt was originally literal, to get it into one's stomach (1839), figurative use by 1931. To tighten (one's) belt "endure privation" is from 1887.