means The process of darkening or coloring the skin through exposure to sun or UV light — or, separately, the craft of turning animal hide into leather.

from From the Old English 'tannian,' to convert hide into leather, which traces back to Medieval Latin 'tannare,' likely from 'tannum,' meaning crushed oak bark — the tannin-rich stuff once used to cure skins. Both meanings share that root: leather and sunbathing alike involve a hide turning brown. The skin-bronzing sense is the younger cousin, blooming only once a tan stopped meaning 'peasant who labors outdoors' and started meaning 'person wealthy enough to vacation in the sun.'