what is paramecium
paramecium noun [C]. âº a âtype of âprotozoan (= an âorganism with only one âcell) that âlives in âwater and âswims by âmoving âstructures âsimilar to âhairs that are âattached to âits âbody. (Definition of paramecium from the Cambridge Advanced Learners Dictionary & Thesaurus Â© Cambridge University Press).