amoeba

n. microscopic protozoan which perpetually changes form

Alternate meanings: Amoeboid, Amoebozoa Amoeba (sometimes amœba or ameba, plural amoebae) is a genus of protozoa that moves by means of temporary projections called pseudopods, and is well-known as a representative unicellular organism. The word amoeba or ameba is variously used to refer to it and its close relatives, now grouped as the Amoebozoa, or to all protozoa that move using pseudopods, otherwise termed amoeboids. The amoeba was first discovered by August Johann Rösel von Rosenhof in 1755.
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Noun
1. naked freshwater or marine or parasitic protozoa that form temporary pseudopods for feeding and locomotion
(synonym) ameba
(hypernym) rhizopod, rhizopodan
(hyponym) endameba
(member-holonym) Amoebida, order Amoebida, Amoebina, order Amoebina

(n.)
A rhizopod. common in fresh water, capable of undergoing many changes of form at will. See Rhizopoda.
  

noun
form of animal life, made up of a single cell
(NOTE: plural is amoebae. Note also the US spelling ameba)

US = AMOEBA