1. A single-celled (protozoan) organism that constantly changes shape.
2. A single-celled organism found in water and in damp soil on land, and as a parasite of other organisms.

Lacking a fixed form and supporting structures, an amoeba consists of a protoplasmic mass in a thin membrane, and forms temporary projections pseudopodia in order to move.

Ameba can infect the bowels to cause diarrhea and the liver to cause abscess formation.

3. Etymology: from the Greek amoibe, "change".