Victory achieved at such great cost that it is nearly a defeat. Pyrrhic is an allusion used almost exclusively in the phrase "Pyrrhic victory,” meaning a victory with losses or costs so great, it's no victory at all.

Because it's derived from a proper name it’s usually capitalized. Uncapitalized and used as a noun it can refer to a war dance perhaps from Purrikhos, supposed inventor of the ancient Greek military dance. Done in quick time it incorporated the movement of actual warfare performed in armor to a musical accompaniment of a flute. Dance, according to Greek thought, was educational and civilizing.

    "The Pyrrhic dance of our time seems to be a sort of Dionysiac dance, being more respectable than that of early times, for the dancers have thyrsi instead of spears, and hurl them at one another, and carry fennel-stalks and torches" (Athenaeus 14.631b).
One researcher relates that :
    (A)rmed dances are attested early and continue throughout antiquity, but the names and types were legion. "Pyrrhiche" was (or became) both the name of a specific kind of dance and a general name for armed dance.

    At Athens the pyrrhiche was associated (e)specially with Athena, for she was said to have invented it after her victory over the Giants or the Gorgon. At the Panathenaia, choruses of boys, of youths, and of men competed in separate pyrrhic contests.

The pyrrhic is also or a metric foot of two syllables in poetry comprising two unaccented syllables typically used to speed up the rhythm of a poem.

Arguably, every victory in war is Pyrrhic because the costs of any battle are always too great. Pyrrhic victories often win the battle but lose the campaign. Retribution is generally Pyrrhic in that, having achieved it, the retaliator feels sympathy for his victim.

The eponym of this word is Pyrrhus (318-272 BC), from the victory of Pyrrhus, a Greek king of Epirus who battled the Roman Empire. Having secured his throne in 297, he then pursued a daring strategy of expansion in support of Tarentum against Rome but his empire was short-lived. He defeated the Romans; at Heraclea in 280 and after invading Italy, he defeated the Romans at Asculum in Apulia in 279. Suffering such staggering loses he was finally forced to withdraw. Even though Pyrrhus was victorious in this first great clash between the Greeks and Romans, it was at the terrible cost of most of his best troops and officers. He is quoted after this second battle in Plutarch's Life of Pyrrhus as saying, "One more victory like this will be the end of me."

Pronounced PEER-ick the adjective strangely enough wasn't used as a picturesque figure of speech based on this two thousand year old episode didn't show up in general English usage until 1885. Today it still means being right may not be worth the fight. As in: “ Winning an argument at the cost of creating rifts between friends is a Pyrrhic victory. “

Sources:

Bryn Mawr Classical Review 2000.03.17:
ccat.sas.upenn.edu/bmcr/2000/2000-03-17.html

yourdictionary.com:
http://www.yourdictionary.com/

Word Detective:
www.word-detective.com

Xrefer:
http://w1.xrefer.com/