1560s, "heliotrope," from sun (n.) + flower (n.). In reference to the Helianthus (introduced to Europe 1510 from America by the Spaniards) it is attested from 1590s, so called from the appearance of the heads.
sun-dress
sun-dried
sundries
sundry
sunfish
sunflower
sung
sunglasses
sunk
sunken
sunless