verb

• (intransitive) To become bigger, especially due to being engorged.
  "O for a Muse of fire, that would ascend The brightest heaven of invention, A kingdom for a stage, princes to act And monarchs to behold the swelling scene!"
• (transitive) To cause to become bigger.
  "Rains and dissolving snow swell the rivers in spring."
• (intransitive) To grow gradually in force or loudness.
  "The organ music swelled."
• (transitive) To cause to grow gradually in force or loudness.
  "It commenced with a slow crescendo, so irresistibly lugubrious that two of our dogs at once raised their heads and swelled their voices into a responsive tremolo, which may have been heard and appreciated by their distant relatives."

noun

• (music) A gradual crescendo followed by diminuendo.
  "He was thinking; but the glory of the song, the swell from the great organ, the clustered lights, […], the height and vastness of this noble fane, its antiquity and its strength—all these things seemed to have their part as causes of the thrilling emotion that accompanied his thoughts."
• (music) A device for controlling the volume of a pipe organ.
• (music) A division in a pipe organ, usually the largest enclosed division.
• (geology) An upward protrusion of strata from whose central region the beds dip quaquaversally at a low angle.

adj

• (dated) Fashionable, like a swell or dandy.
  "We pay the express, $5 a day our new agents are making and wearing the swellest clothes besides; old agents after one season make twice as much."
• (Canada, US, dated slang) Excellent.
  "...you are my devoted friend too. You do more and work harder and oh shit I'd get maudlin about how damned swell you are. My god I'd like to see you... You're a hell of a good guy."

adv

• (Canada, US, informal) Very well.
  "“That lousy ring wasn’t worth no grand. I did swell to get two centuries for it.”"