Past tense of balloon; grew or swelled rapidly in size, amount, or importance.
From 'balloon,' which came from Italian 'pallone' (large ball), entering English in the 17th century after the Montgolfier brothers' famous 1783 flight.
When economists say 'the national debt ballooned,' they're using the same word that described humankind's first successful aircraft—the metaphor perfectly captures rapid, uncontrolled growth.
Complete word intelligence in one call. Free tier — 50 lookups/day.