Dictionary.com
Thesaurus.com

knees-up

American  
[neez-uhp] / ˈnizˌʌp /

noun

British Informal.

  1. a party or lively gathering, usually including dancing.

knees-up British  

noun

  1. a boisterous dance involving the raising of alternate knees

  2. a lively noisy party or celebration, esp one with dancing

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of knees-up

By ellipsis from Knees up, Mother Brown a popular dance, originally a song with the same title (1939)

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.