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shanks's pony

British  
/ ˈʃæŋksɪz /

noun

  1. informal one's own legs as a means of transportation

"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 shanks's pony

C18: from shank (in the sense: lower leg); probably with a pun on the surname Shanks