any chiefly marine protozoan of the sarcodinian order Foraminifera, typically having a linear, spiral, or concentric shell perforated by small holes or pores through which pseudopodia extend.
1835, Mod.L., neut. pl. of foraminifer "bearing holes," from L. foramen "hole, opening, orifice" + -fer "bearing;" so called because the shells are usually perforated by pores.