na-adjective, noun
relaxed; carefree; comfortable; unconstrained
Describes a person, manner, voice, movement, or atmosphere that feels free, relaxed, and not cramped or tense. Often used as 伸びやかな, 伸びやかに, or 伸びやかだ.
子どもたちは広い園庭で伸びやかに遊んでいる。
The children are playing freely in the spacious schoolyard.
彼女の伸びやかな歌声が会場に響いた。
Her relaxed, free-flowing singing voice echoed through the hall.