Lynn, as far as I know a weeder has a handle like 2 meter long with a very small gasoline motor and it is used for cutting grass, it does not use metal blades but a nylon cord like the ones used for fishing, the nylon cord rotates very fast and also has to be changed very soon. A mower is a machine with a gasoline motor and metal blades and you have to push it. I hate it. Reaper is normally used in figurative language to symbolize death coming for the marked ones, you will find excellent and difficult English about it in Edgar Allen Poe works. Harvester can be used to refer to a person, but also to a big machine used to harvest the crops. There is a company with the brand name Harvester which manufactures big trucks and agricultural machines. Hope it helps.