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undertrump

American  
[uhn-der-truhmp, uhn-der-truhmp] / ˌʌn dərˈtrʌmp, ˈʌn dərˌtrʌmp /

verb (used with or without object)

Cards.
  1. to trump with a lower trump than has already been played.


undertrump British  
/ ˌʌndəˈtrʌmp /

verb

  1. (intr) cards to play a lower trump on a trick to which a higher trump has already been played

"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 undertrump

First recorded in 1860–65; under- + trump 1