Definition of tagma:
(n) :
(morphology of segmented Metazoa) A specialized, structured, grouping of functionally related segments, or analogous subunits, into units such as the head, the thorax, and the abdomen, particularly in various Arthropoda and Vertebrata.
(n) :
(physiology, dated) A specialized, structured, grouping of functionally related molecules, forming the basis the physiology and structure of larger units such as cells and tissues.
(n) :
(historical) A military unit of battalion or regiment size, in the Byzantine empire of the 8th - 11th centuries.