taru-adjective, adverb taking the 'to' particle
Literary adjective/adverb describing a bright, clear light, especially moonlight. Often used in classical or poetic contexts.
皓々と輝く月が、静かな湖面を照らしていた。
The brightly shining moon illuminated the quiet surface of the lake.
taru-adjective, adverb taking the 'to' particle
broad and empty; vast and desolate
Rare literary use describing a wide, empty expanse, often with a sense of loneliness. May appear in classical descriptions of landscapes.
荒野は皓々として、人影ひとつなかった。
The wilderness stretched out broad and empty, without a single soul in sight.
The kanji 皓, 皎, and 晧 all share the meaning 'bright, white, clear' and are used in reduplicated form to create a literary adjective/adverb. The exact historical derivation is uncertain, but the reduplication pattern is common in classical Japanese for emphasis.