The word 'sunbathe' is a modern English compound, first attested in the late 19th century. It is formed by combining the noun 'sun', referring to the celestial body, with the verb 'bathe', which originally meant to wash or immerse oneself in liquid. The formation employs a vivid metaphorical shift: just as one bathes in water, one can be immersed in the rays of the sun. This lexical blend perfectly captures the leisurely activity of exposing one's body to sunlight for pleasure or to darken the skin, reflecting a cultural practice that gained popularity in the early 20th century.

Structure: sun (star) + bathe (wash) - sun: From Old English sunne, of Germanic origin; related to Dutch zon and German Sonne. In this compound, it functions as a noun denoting the source of light and heat. - bathe: From Old English baþian (to wash, immerse in water), from bæþ (bath). In this compound, it functions as a verb, but its meaning is extended metaphorically from "washing in water" to "immersing in sunlight."