the undulating movement of the surface of the open sea
"The calm afternoon allowed us to watch the swell roll gently toward the shore without any whitecaps breaking over it."
a rounded elevation (especially one on an ocean floor)
"The sudden drop in water level revealed a massive swell of sand rising from the ocean floor."
a crescendo followed by a decrescendo
"The crowd's cheers swelled to a deafening roar and then suddenly faded into silence when the referee blew the final whistle."
a man who is much concerned with his dress and appearance
"He spent an hour in front of the mirror adjusting his tie before arriving at the gala, proving he was such a swell."
The act of swelling; increase in size.
"The swollen ankle made it difficult for him to walk after his long hike through the marshland."
To become bigger, especially due to being engorged.
"After spending hours in the hot sun, my lips began to swell from dehydration."
Fashionable, like a swell or dandy.
"He dressed up to look particularly swell for the gala."
Very well.
"I thought you might be able to swell by about ten percent if we add a few more items to your order."
The word "swell" comes from Old English, where it originally meant to expand or increase in size. Its ultimate origin is unknown, though it shares roots with similar words in other Germanic languages like Dutch and German.