na-adjective
Describes speech, writing, or expression that is succinct and to the point, without unnecessary detail.
彼の説明はつづまやかでわかりやすい。
His explanation is concise and easy to understand.
彼女はつづまやかな生活を送っている。
She leads a frugal life.
na-adjective
Describes a person's demeanor or behavior as understated, not drawing attention to oneself; can also apply to appearance or manner.
彼はつづまやかな態度で賞を受け取った。
He accepted the award with a modest attitude.
簡潔 is the standard word for 'concise' and is more common in modern Japanese; つづまやか is a more literary or refined alternative.
Derived from the classical verb 約む (つづむ) meaning 'to abridge' or 'to be frugal', with the adjectival suffix やか. The exact historical development is uncertain, but the kanji 約 reflects the core meaning of reduction or restraint.