Which word derives from the root primus?

a. posthumous

b. principal

c. printing

d. primate

The correct answer is primate!

Primate used to mean a rank in religious hierarchy, (which later was used as an inspiration for the biological term).

This word comes from Latin Primat and Primus, meaning first rank, or simply "first".

Principal comes from principalis, just like prince, rather than "primus".