If you describe a victory as a Pyrrhic victory, you mean that although someone has won or gained something, they have also lost something which was worth even more.
Pyrrhic victory in British English
noun
a victory in which the victor's losses are as great as those of the defeated
Also called: Cadmean victory
Word origin
named after Pyrrhus, who defeated the Romans at Asculum in 279 bc but suffered heavy losses
Pyrrhic victory in American English
(ˈpɪrɪk; ˈpɪrɪk)
a too costly victory
in reference to either of two victories of Pyrrhus, king of Epirus, over the Romansin 280 and 279 b.c., with very heavy losses
Word origin
Gr Pyrrhikos
Examples of 'Pyrrhic victory' in a sentence
Pyrrhic victory
only after I'd won my Pyrrhic victory did I stop to wonder why I was so determined to get back to East Anglia.
Harris, Elizabeth TIME OF THE WOLF (2001)
"The kinds of losses we're suffering, I don't know who'll be left to enjoy even a Pyrrhic victory.