A bootlace is the long cord you thread through the holes or hooks of a boot and pull tight so the boot stays on. It is the same idea as a shoelace, but made for a boot, so it is often longer and a bit thicker. British English likes this word; American speakers will often say shoelace even when the footwear is a boot. You hear it in ordinary talk about getting dressed, walking, work boots, and football boots. A bootlace can come undone, snap, or be replaced. There is also a fashion thing called a bootlace tie — a very thin necktie that looks like a lace — but that is a stretch of the same picture, not the everyday meaning. The everyday meaning is simply the string that fastens a boot.