Answer: rerum

AnswerCrossword Clue
RERUM... primordial: the first beginnings of things.
RERUMIn ... natura (in the nature of things): Lat.
RERUM... primordia (first beginnings of things): Lat.
RERUM... primordia (first beginnings of things).
RERUM... novarum
RERUM"De ... Natura," Lucretian opus