The word daisy is from Old English dæges éage, meaning day’s eye.

This name alludes to the fact that the flower of this plant opens in the morning and closes at night, as the human eye does. Perhaps its petals, which close over its bright centre at the end of the day, were also thought to resemble human eyelashes.

But the name also alludes to the flower’s appearance. In his 1889 edition of Chaucer’s Legend of Good Women, the English philologist Walter William Skeat (1835-1912) wrote:

The primary meaning of dæges éage is doubtless the sun; the daisy is named from its supposed likeness to the sun, the white petals being the rays, and the yellow centre the sun’s sphere.

Indeed, in Troy Book (1412-20), the monk and poet John Lydgate (circa 1370 – circa 1451) thus described Apollo, god of the sun:

And nexte Appollo, so cler, so schene & briȝt,
Þe daies eye & voider of þe nyȝt.
     translation:
And next Apollo, so clear, so resplendent and bright,
The day’s eye and remover of the night.

The English poet Geoffrey Chaucer (circa 1342-1400) wrote about the daisy in The Prologue to The Legend of Good Women. He mentioned the etymology of the word:

               to loke upon the dayesie,
That wel by reson men it calle may
The ‘dayesye’, or elles the ‘ye of day’,
The emperice and flour of floures alle.
     translation:
               to look upon the daisy,
That for good reason men do name
The ‘day’s eye’ or else the ‘eye of day’,
The Empress, and flower of flowers all.

And Chaucer described how the flower closes and opens:

As sone as evere the sonne gynneth weste,
To seen this flour, how it wol go to reste,
For fere of nyght, so hateth she derknesse.
Hire chere is pleynly sprad in the brightnesse
Of the sonne, for ther yt wol unclose.
     translation:
As soon as ever sun sinks in the west
To see this flower, how she does sink to rest
For fear of night, she so hates the darkness.
Her face is wholly open to the brightness
Of the sun, for there it does unclose.

The phrase to be (as) fresh as a daisy, meaning to be healthy and full of energy, comes perhaps from the fanciful assumption that the daisy is never tired because it ‘sleeps’ regularly.

It is first recorded in a letter by ‘Corrigidor’ [= Chastiser] about coffee-house loungers, published in The Town and Country Magazine; or, Universal Repository of Knowledge, Instruction, and Entertainment (London) of November 1778:

Harry Bluster no sooner enters the room, than he gives, “A yoy ho! yoy―yoy my boys―here I am, sound wind and limb―fresh as a daisy, came a hundred miles yesterday―nothing stopt, five-barred gates and all; they took me at one place for the flying highwayman.”

The French equivalent of daisy is the feminine pâquerette, probably from Old and Middle French pasquis (Modern French pâquis), pasture, and the diminutive suffix -ette, because pastures are dotted with daisy flowers.

According to an alternative, and dubious, etymology, pâquerette is from Pâques, Easter, and the diminutive suffix -ette, supposedly because the plant flowers during the Easter period, which is erroneous since it has flowers nearly all year round.

The French equivalents of (as) fresh as a daisy are, to describe a male person, frais comme un gardon, fresh as a roach (i.e. the freshwater fish of the carp family), and, to describe a female person, fraîche comme une rose, fresh as a rose (an image also used in English, by Chaucer for example).