The noun holster looks like holder and that's exactly what it is. Some holsters hold a single item, like a gun, and others are more like tool belts, holding many small items.
The o in holster is long, so pronounce it like this: "HOLE-ster." Originally, the word described something very specific — a leather case for a pistol. It probably comes from the Old English word heolster (earlier helustr), which means "concealment, hiding place." Today, holsters may hide what they hold, but they always keep things handy.
