The word 深夜 is formed by combining the character for 深 (shēn), meaning "deep", with the character for 夜 (yè), meaning "night". It is a direct and evocative conceptual compound where the quality of "depth" is applied metaphorically to the temporal dimension of night, picturing the night not just as a time of day but as a profound, quiet, and advanced period within it, the deepest, darkest, and most still hours when the night is at its fullest.