The word "sunny" is a transparent compound formed within English from its native Germanic elements. Its first element, "sun," descends directly from the Old English sunne, which itself originates from the Proto-Germanic sunnōn, a feminine noun. This Germanic root is further traced back to the Proto-Indo-European sóh₂wl̥, the shared ancestor for the concept of the sun across many languages, including Latin sōl and Greek hēlios. The suffix "-y," also of Germanic heritage, is added to the noun to create an adjective meaning "abounding in" or "resembling" the sun. Thus, the literal meaning "full of sunshine" logically extended to describe both bright, clear weather and, metaphorically, a bright and cheerful disposition.

Structure: sun (the star) + y (adjective suffix) - sun: From Old English sunne, of Germanic origin; related to Dutch zon and German Sonne. The core noun referring to the celestial body. - y: A productive English suffix of Germanic origin, used to form adjectives from nouns, meaning "characterized by" or "full of."