SEIL, an isle, in the parish of Kilbrandon, county of Argyll. This is an isle of the Hebrides, about two miles in length and three in breadth, separated from the island of Easdale by a strait a few hundred feet broad, and from the main land by a narrow pass over which is a bridge. It is in general flat, yet not altogether without hills, from the higher of which is a fine view of the numerous small isles scattered over the ocean in these parts, with the distant mountains of Mull and Jura. Here are several slate-quarries, but those of the island of Easdale are more valuable.