According to Britannica, most of us tend to use the terms interchangeably, and we tend to associate “ethical” behaviour with professions (like law, medicine, and engineering).
Ethicists today, however, use the terms interchangeably. If they do want to differentiate morality from ethics, the onus is on the ethicist to state the definitions of both terms. Ultimately, the distinction between the two is as substantial as a line drawn in the sand.
The way I understand it is: We mostly agree that gay marriage is ethical. However, it may be immoral to an adherent of a religion that proscribes it (but would they agree that it is ethical?)