bulging

The verb 'bulge' entered middle english from old french 'bougier', meaning 'to swell or curve outwards', which itself likely derived from a vulgar latin root 'bullicāre', 'to bubble or boil'. This latin term finds its origin in the latin 'bullīre', meaning 'to boil', which is connected to 'bulla', a word for a bubble or a rounded swelling. The semantic journey from the concept of bubbling liquid to a protuberant shape is clear, with the '-ing' suffix then forming the adjective describing something that possesses this swollen, protruding quality.

The word 'bulging' is the present participle/adjective form of the verb 'bulge'. It is treated as a simplex unit for morpheme analysis as segmenting 'bulg-' and '-ing' would separate a derivational suffix from a root that is not independently meaningful in modern english.