1Biology. A (relatively large) encysted stage of the life cycle in a slime mould; specifically a thick-walled, multinucleate structure formed as part of the sexual cycle in certain slime moulds of the phylum Dictyostelida.
2Medicine and Pathology. A macroscopic cyst; a large cyst.
3Veterinary Med. A macroscopic sarcocyst.
Origin
Late 19th century (in an earlier sense). In sense 1 from French macrocyste from macro- + -cyste; compare paracyst.