taru-adjective, adverb taking the 'to' particle
Literary word describing a solitary, forlorn state, often with a nuance of helplessness. Used with たる or として.
彼は孑然として荒野に立っていた。
He stood alone and helpless in the wilderness.
孑然たる孤島に流れ着いた。
He was washed ashore on a solitary, isolated island.