taru-adjective, adverb taking the 'to' particle
A literary 'taru' adjective describing a broad, open, or boundless expanse, often of land, sky, or a state of mind. Rare in modern Japanese; mainly encountered in classical or formal writing.
曠然たる平原が目の前に広がっていた。
A vast plain stretched out before my eyes.
彼の心は曠然として、一点の曇りもなかった。
His mind was open and clear, without a single cloud.
Composed of 曠 (vast, empty) and 然 (a suffix forming adjectives/adverbs indicating state). The exact historical derivation is uncertain; the word follows a classical Chinese-derived pattern for literary adjectives.