 A composite thing has more than one part. The verb fuse refers to an asymmetric relation between a whole and its parts. If two things fuse they ‘join together’ to make up a whole. For example, if the water in my glass and the water in your glass fuse, then there exists a thing, a fusion, which is made up of the two portions (sometimes it is said that the two portions ‘have a fusion’). No literal contact or fusion (e.g., welding two rods together) is implied by this usage. If a fleet is a single thing, then it is arguably a fusion of the boats making it up. The nouns whole and sum are synonymous with fusion and composite. Overlap occurs when distinct things share one or more parts.