registrant (n.)

late 14c., registren (transitive), "to record, enter in a listing," from Old French registrer "note down, include" (13c.) and directly from Medieval Latin registrare, from registrum (see register (n.1)). From c. 1400 as "to enroll (someone) in a listing."

Intransitive sense, of instruments, is from 1797; of persons and feelings, "make an impression," by 1901. Meaning "to enter one's name in a list" for some purpose (as a voter, as a guest at a hotel, etc.) is by 1848. Related: Registered; registering. Registered nurse attested from 1879.

agent or instrumental suffix, from Old French and French -ant, from Latin -antem, accusative of -ans, present-participle suffix of many Latin verbs. Compare -ance.