An old, literary word for a young man from the countryside — usually a young farm worker or shepherd — who is in love with a young woman. You will almost never hear it in speech today. You meet it in old poems and old songs, especially the kind about shepherds and country love, and in phrases like 'a country swain' or 'her swain'. There is a second, older use you may see in very old texts: a servant or a young male attendant, with no love in it at all; the 'man in love' meaning grew out of the pastoral poems where the shepherd boy is always sighing over some girl. Because it belongs to that old poetic world, when someone uses 'swain' today it is nearly always a joke, or a deliberate old-fashioned touch — a man teasing his friend, 'and here comes your swain'. It carries a gentle, slightly silly sweetness: the swain is sincere but a bit hopeless, standing there with flowers. Note that it is the man who is the swain; the woman he loves is not one. There is also a fixed phrase, 'a boating swain' — no, be careful here: the sailing word is 'boatswain' (said 'BOH-sun'), one word, and it means the sailor in charge of the equipment on a ship. That is a different word that happens to end the same way.