The word 'yellowing' is a transparent English formation built upon the ancient color term 'yellow'. The root 'yellow' descends from the Proto-Germanic 'gelwaz', which itself can be traced back to the Proto-Indo-European root 'ghel-', meaning 'to shine'—a root that gave rise to a family of words for colors like yellow and green, associated with brightness and vegetation. The addition of the '-ing' suffix, a productive morpheme inherited from Old English '-ung'/-'ing', transforms the adjective/verb into a noun denoting the process or result of the action. Thus, the literal construction "the process of becoming yellow" directly and logically conveys its modern meaning, describing the gradual acquisition of a yellow hue, often due to age, decay, or chemical change.

Structure: yellow (color) + ing (noun/adjective suffix) - yellow: From Old English 'geolu', 'geolwe' (yellow), of Germanic origin; related to Dutch 'geel' and German 'gelb'. Functions as the base adjective/color term. - ing: A suffix of Germanic origin, used in English to form verbal nouns (gerunds) and present participles, which can also function as adjectives. In this word, it indicates the process or state of the action described by the base verb ('to yellow').