"swelling up," 1796, from Latin intumescentem (nominative intumescens), present participle of intumescere "to swell up, rise, be elevated," of sounds, "grow louder," figuratively, "grow excited, become enraged," from in- "in" (from PIE root *en "in") + tumescere "begin to swell, swell up," figuratively "grow excited, become enraged," inceptive of tumere "to swell" (from PIE root *teue- "to swell"), with inchoative suffix -escere.
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