Seemly means suitable for that moment and that company — what accepted manners would allow. Loud jokes at a funeral are not seemly; a short dress might not feel seemly at a formal ceremony. It is quite old-fashioned and formal. Younger people almost never say it in daily talk; you are more likely to meet it in books, or in the living opposite unseemly (too loud, too sexual, too rude for the occasion). It is about behaviour and taste, not about whether something looks true. Though actually, it is built like seem + -ly, but it does not mean “in a seeming way.” That meaning belongs to seemingly. Seemly came into English from Old Norse, in the sense of what befits you, what is fitting.

得體的；合宜的（偏書面、老派）