/pruy mawr"dee euhm/ , n. , pl. primordia /-dee euh/ . Embryol.
the first recognizable, histologically differentiated stage in the development of an organ.
[ 1665-75; primordium, in pl.: beginnings, elementary stage, equiv. to prim ( us ) first (see PRIME) + ord ( iri ) to begin + -ium -IUM; cf. EXORDIUM ]