The compound adjective 'white-capped' is a relatively modern English formation, combining two native Germanic roots. The first element, 'white', descends from the Proto-Germanic hwītaz, which itself derives from the Proto-Indo-European root ḱweyt- meaning 'to shine' or 'bright'. The second element, 'cap', originates from the Late Latin cappa, entering Old English and evolving to denote a head covering or topmost part. The suffix '-ed' is a productive adjectival suffix in English, used to indicate possession of a quality. Thus, the literal logic of 'having a white top' is applied descriptively, most commonly to natural phenomena like ocean waves whose crests break into white foam or mountain peaks covered in snow.

Structure: white (color) + cap (top/cover) + ed (adjective suffix) - white: From Old English hwīt, of Germanic origin; related to Dutch wit and German weiss. Functions as a descriptive adjective root meaning the color white. - cap: From Old English cæppe, from Late Latin cappa 'hood'. Functions as a noun root meaning a covering or top. - ed: From Old English -ed, -od, -ad, a suffix forming adjectives from nouns, meaning 'having' or 'provided with'.