prerogative

1350–1400; Middle English < Latin praerogātīvus (adj.) voting first, praerogātīva (noun use of feminine of adj.) tribe or century with right to vote first. See pre-, interrogative

1. See privilege.

The English noun prerogative has always been a legal or political term, first in Latin, then in Old French and Anglo-French. In Latin, praerogātīva was the tribe or century (a company of soldiers, also one of the units into which Roman citizens were assigned for voting) to which the first vote fell by lot (this vote was counted before the other centuries or tribes voted and was very influential).
Praerogātīva also meant “the verdict or vote of this tribe or century; a prior verdict, election, right, or claim.” Medieval Latin developed the sense ““a previous choice, sure sign, special right, privilege,” and in Anglo-French and Old French prerogative meant “a privilege accorded to certain dignitaries, a special right or privilege exercised by the monarch.” By the early 15th century, Middle English prerogative meant “a precedence, superiority, or preeminence,” a meaning now obsolete. The common thread that remains in the current senses of the word in English are aspects of meaning related to a right, privilege, or power.