time; the passage of time
Literary and somewhat old-fashioned; often used in set phrases like 光陰矢の如し (time flies like an arrow). The personification 'Father Time' is a possible translation in poetic contexts.
They say time flies like an arrow, and a year really does pass in the blink of an eye.
Time waits for no one; before I knew it, it's already autumn.
photocathode
From Chinese 光陰／光阴 (guāngyīn), literally 'light and shadow', a metaphor for the alternation of day and night and thus the passage of time.