na-adjective
Describes a pleasantly cool, refreshing feeling, often associated with a breeze, sound, or appearance. Can also describe a clear, bright quality, such as a voice or expression.
涼やかな風が窓から入ってきた。
A refreshing breeze came in through the window.
彼女の涼やかな声
Her clear voice echoed through the room.
涼しい is the common i-adjective for 'cool' (weather, temperature). 涼やか is a na-adjective with a more poetic, sensory nuance, often used for sounds, appearances, or a refreshing atmosphere.
Derived from the stem 涼 (suzu-) of the classical adjective 涼し (suzushi), combined with the suffix やか (-yaka), which forms na-adjectives expressing a state or quality. The exact historical development is uncertain, but the word has been used since classical Japanese to describe a refreshing coolness.