from The American Heritage® Dictionary of the English Language, 4th Edition
- intransitive v. To play a trump lower than another card player's trump when trump has not been led.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- v. To play a lower trump card than the previous one in a trick.
from The Century Dictionary and Cyclopedia
- To throw a trump to, as a non-trump lead of cards in whist, lower than one already thrown by one's partner.
Sorry, no etymologies found.
He kept on taking too many tricks as I seemed to be able to undertrump him the entire game.