adverb, adverb taking the 'to' particle
calmly; peacefully; painlessly; comfortably
Rare literary adverb describing an action done without difficulty, stress, or pain. Often used with verbs like 眠る, 暮らす, or 死ぬ. In modern Japanese, 安らかに or 楽に are more common.
祖母は安々と眠りについた。
My grandmother passed away peacefully.
彼は安々と暮らしている。
He lives comfortably and without worry.
楽 is a common na-adjective/adverb meaning 'easy' or 'comfortable'. 安々 is more literary and often implies a serene, untroubled quality rather than just ease.
Reduplication of 安 (yasu, 'peaceful, easy') with the adverbial suffix 々. The exact historical derivation is uncertain, but it follows a pattern of forming adverbs from adjective stems.