Why is the ninth month called September?
1520s, originally "to move confusedly," perhaps coined on model of stumble, tumble, etc. In 17c., it was yet another euphemism for "have sex with" (a sense first attested 1580s). Meaning "mix or confuse" is from 1540s. Related: Jumbled; jumbling.
"a confused mixture," 1660s, from jumble (v.).