adverb taking the 'to' particle, taru-adjective
resolutely; with spirit; courageously
Literary adverb describing a spirited, determined manner of action. Often used with と (to) to modify a verb, as in 奮然と立ち上がる (rise resolutely).
彼は奮然と立ち上がり、反論を始めた。
He rose resolutely and began his rebuttal.
困難に直面しても、奮然たる態度を崩さなかった。
Even when facing difficulties, he maintained a resolute attitude.
Compound of 奮 (fun, 'stir up, rouse') and 然 (zen, a suffix forming adjectival adverbs). The exact historical derivation is uncertain, but the word follows a classical Chinese pattern for forming literary adverbs.