"to dismiss lightly and contemptuously," literally "to turn aside with an exclamation of 'pooh,'" 1827, a slang reduplication of dismissive expression pooh. Among the many 19th century theories of the origin of language was the Pooh-pooh theory (1860), which held that language grew from natural expressions of surprise, joy, pain, or grief.
1560s, "to leap up;" 1590s, "to rejoice, triumph," from French exulter, from Latin exultare/exsultare "rejoice exceedingly, revel, vaunt, boast;" literally "leap about, leap up," frequentative of exsilire "to leap up," from ex "out" (see ex-) + salire "to leap" (see salient (adj.)). The notion is of leaping or dancing for joy. Related: Exulted; exulting.
late 14c., "tendency to change, inconstancy," from Old French mutabilité, from Latin mutabilitas, from mutabilis "changeable" (see mutable).
It is the same!—For, be it joy or sorrow,
The path of its departure still is free;
Man's yesterday may ne'er be like his morrow;
Nought may endure but Mutability.
[Shelley, from "Mutability," 1816]