Answer: Ameoba is a single-celled animal that catches food and moves about by extending fingerlike projections of protoplasm. Amoebas are either free-living in damp environments or parasitic. Amoeba: Also ameba. A single-celled (protozoan) organism that constantly changes shape. The word "ameba" is from the Greek "amoibe" meaning "change." Ameba can infect the bowels to cause diarrhea and the liver to cause abscess formation.