The definition is Musical show, referring to the Gilbert and Sullivan comic opera *Iolanthe*. The wordplay builds from "one" giving I (Roman numeral), "advance" giving LOAN, and "article" giving THE, which together form I + LOAN + THE. "Oscar" represents O (from the NATO phonetic alphabet), and "promoted" (in a down clue) means it moves up one position within that string. So the O shifts up one spot from its place in LOAN, jumping ahead of the L, turning I-L-O-A-N-T-H-E into I-O-L-A-N-T-H-E — IOLANTHE.