bedfast is a compound of bed + fast in the sense 'fixed, firmly held' (as in steadfast). Fast derives from Old English fæst ('firm, fixed'), from Proto-Germanic *fastuz. Morphologically, the word is transparent as a compound: its parts remain visible in the modern spelling, while the older history of those parts supplies the deeper ancestry. In modern use, the adjective sense is "confined to bed by illness; bedridden", which keeps the etymology connected to the word's present dictionary value rather than treating it as a merely historical label. The wider word family includes related English forms such as bed, steadfast, bedridden, showing how the same base continues to support neighboring English vocabulary. The principal historical forms in the chain include Old English bedd, Old English fæst, which anchor the explanation in named linguistic material.