To increase in size or volume as a result of internal pressure; expand. To increase in force, size, number, or degree: Membership in the club swelled. To grow in loudness or intensity: "The din in front swelled to a tremendous chorus\u201d ( Stephen Crane). To bulge out, as a sail. To rise or extend above the surrounding level, as clouds. To rise in swells, as the sea. To be or become filled or puffed up, as with pride, arrogance, or anger. To rise from within: Rage swelled within me. To cause to increase in volume, size, number, degree, or intensity: The governor's full public disclosure only swelled the chorus of protests. To fill with emotion. The act or process of swelling. The condition of being swollen. A swollen part; a bulge or protuberance. A long wave on water that moves continuously without breaking. A rise in the land; a rounded elevation. Informal One who is fashionably dressed or socially prominent: society swells. Music A crescendo followed by a gradual diminuendo. Music The sign indicating such a crescendo. Music A device on an instrument, such as an organ or harpsichord, for regulating volume. Informal Fashionably elegant; stylish. Informal Excellent; wonderful: had a swell time.