noun. organisms without vascular tissue: e.g. algae, lichens, fungi, mosses.
noun. any organism of microscopic size.
noun. ['ˈɔrgəˌnɪzəm'] a living thing that has (or can develop) the ability to act or function independently.
noun. ['ˈɔrgəˌnɪzəm'] a system considered analogous in structure or function to a living body.