1. A single-celled (protozoan) organism that constantly changes shape.>BR? 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.

The word ameba is from the Greek amoibe meaning "change".