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Webster 1913 Edition

Noun.

Anything moved with a whirl, as preparatory for a blow, or to augment the force of it; – applied by poets to the cestus of ancient boxers.

The

whirlbat

and the rapid race shall be
Reserved for Caesar.

Dryden.

whirlbat ‎(plural whirlbats)

(archaic) Anything moved with a whirl, as preparatory for a blow, or to augment the force of it.
(archaic, poetic) The cestus of ancient boxers.