amain comes from a- ('in, with') + main ('strength, force'), from Old English mægen ('strength, power'), from Proto-Germanic *maginą. 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 adverb sense is "at full speed or with great force; vehemently", 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 main, might, showing how the same base continues to support neighboring English vocabulary. The principal historical forms in the chain include Old English mægen, Proto-Germanic *maginą, which anchor the explanation in named linguistic material.