'baysmelt' originates from English, a compound of the noun 'bay' and the noun 'smelt', where 'bay' referred to a coastal inlet and 'smelt' referred to a small silvery fish.

'baysmelt' developed in modern English as the compound 'bay' + 'smelt'; earlier attestations appear as 'bay-smelt' or 'bay smelt', and in some usages the form consolidated into the single-word 'baysmelt'.

Initially it referred more generally to 'smelt' (small oily fishes); over time it came to denote specifically those smelt species associated with bays or estuaries and to function as a common name for such species.