taru-adjective, adverb taking the 'to' particle
dark and desolate; forlorn
Literary or formal term describing a gloomy, lonely atmosphere or state. Often used with と (陰々と) as an adverb.
廃墟は陰々とした雰囲気に包まれていた。
The ruins were enveloped in a dark and desolate atmosphere.
彼は陰々と過去の失敗を語った。
He forlornly recounted his past failures.
陰気 is a more common word for gloomy or melancholy, used as a noun or na-adjective. 陰々 is more literary and emphasizes a desolate, forlorn atmosphere.
Reduplication of 陰 (いん, 'shade, gloom'), emphasizing a state of deep gloom or desolation. The exact historical derivation is uncertain.