adverb taking the 'to' particle, taru-adjective
quietly; calmly; self-composed
Literary or formal adverb/adjective describing a state of being calm, composed, and unhurried. Often used with と (e.g., 閑々と) or as a たる adjective. The cross-reference 悠々閑々 reinforces the unhurried, leisurely nuance.
See also: 悠々閑々
彼は騒がしい中でも閑々と本を読んでいた。
He was quietly reading a book even amidst the noise.
閑々たる態度で交渉に臨んだ。
He approached the negotiation with a calm and composed attitude.
Reduplication of 閑 (kan, 'quiet, leisure'), forming an adverb/adjective emphasizing a state of calm composure.