Meanings

cesium atomic clock

nuclear fission

atomic clock

agricultural burning

protostar

group (of atoms)

fibrinogen

protohistory (the period between prehistory and history)

primary immunodeficiency syndrome

malaria-causing protozoan (i.e. plasmodium)

aurochs

primary immunodeficiency syndrome

overriding principle

Fujiwara period (esp. used as a period of art history, approx. 894-1185 CE)

Proterozoic era

agglutinogen

thin Japanese paper (used as tissue during the Edo period)

principal cause

original source of re-established family register

antigenic determinant