taru-adjective, adverb taking the 'to' particle
in full bloom; glorious; splendid
Literary taru-adjective describing flowers in full bloom or something at its peak of glory. Often used in the phrase 百花爛漫 (a hundred flowers in full bloom).
春の野山は百花爛漫の美しさだ。
The spring fields and hills are beautiful with a hundred flowers in full bloom.
彼女の笑顔は爛漫と輝いていた。
Her smile was radiantly glorious.
The kanji 爛 means 'be bright' or 'glow', and 漫 means 'overflowing' or 'spreading'. Together they suggest a radiant, overflowing splendor. The exact historical derivation is uncertain, but the word is used in classical and literary Japanese.