taru-adjective, adverb taking the 'to' particle
beautiful; florid
Literary, archaic adjective describing something as strikingly beautiful or richly ornate, often used with たる or と.
彼の文章は斐然たる美しさがある。
His writing has a florid beauty.
その絵は斐然として輝いていた。
The painting shone with striking beauty.