The common English daisy — a small white flower with a yellow centre — carries inside its name an act of close attention. The word is a contraction of the Old English dæges ēage, "the day's eye." The flower closes its petals at night and opens them again at dawn, like an eye blinking awake.
An Old Observation
Anglo-Saxon speakers who named the daisy were noticing something specific: the flower really does open at sunrise and close again at sunset. The yellow centre, ringed by white petals, looks like a small eye watching the day. It is the kind of metaphor that survives best when nobody questions it — and the daisy has been called a "day's eye" so long that almost no English speaker hears the original meaning anymore.
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A Long, Slow Compression
The Old English compound dæges-ēage wore down through Middle English forms like dayeseye, dayseye, and daysie before settling, in the late 14th century, on something close to the modern daisy. By Chaucer's time the word was already a single unit, though Chaucer himself, in The Legend of Good Women, plays with the older meaning, calling the flower "the eye of the day."
Why So Many "-eye" Plant Names?
English has several other plants whose names refer to eyes — eyebright (used in folk medicine for eye complaints), oxeye daisy, pheasant's eye. The visual instinct of medieval naming is hard to miss: round flowers with contrasting centres look like eyes, and the name sticks.