taru-adjective, adverb taking the 'to' particle
quiet and still; without sign of life
Literary taru-adjective describing a scene of deep silence and stillness, often with a sense of emptiness or absence of people. Used in written descriptions, not in everyday speech.
夜の森は闃然として、物音一つしなかった。
The forest at night was utterly quiet and still, without a single sound.
廃墟の街は闃然と静まり返っていた。
The ruined town lay in complete silence, with no sign of life.
The word is composed of 闃 (quiet, still) and 然 (state, manner). The exact historical derivation is uncertain; it is a literary Sino-Japanese term.