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Swinter: The combination of summer and winter together.
Candace: Swinter?!
Phineas: Some people call it wummer.
by lykeomgzzzzzgirl June 26, 2009
A season, especially prominent in the eastern US, characterized by days of winter weather followed by a day of summer weather.
"Damn yesterday it was 70 and sunny but now it's 35 and snowing."

"Yeah man, I guess it's swinter."
by Brunered April 15, 2014