organism UK /ˈɔː.ɡə.nɪ.zəm/US /ˈɔɹ.ɡəˌnɪz.əm/ noun3 •A discrete and complete living thing, such as animal, plant, fungus or microorganism.This strategy, known as caloric restriction, has been shown to increase the life span of various organisms and reduce their rate of cancer and other age-related ailments. — 2019 •Something with many separate interdependent parts, seen as being like a living thing; an organic system.For the first time, Edith was aware of the hotel as a well populated organism, its attendants merely resting until an appropriate occasion should summon them to present themselves […]. — 1984 •(no longer used, rare) The fact of being organic; organicity. formsorganisms