Roman tribes voting first had outsized influence — 'prerogative' (asked before) became any exclusive prior right.
A right or privilege exclusive to a particular individual or class; a faculty or property distinguishing a person or class.
From Latin 'praerogātīva' (the right to vote first; a prior claim), originally the feminine of 'praerogātīvus' (asked first, voting before others). Derived from 'praerogāre' (to ask before, to ask in advance), composed of 'prae-' (before, in front) + 'rogāre' (to ask, to propose a law). The PIE root behind 'rogāre' is *h₃reǵ- (to move in a straight line, to direct, to rule) — the same root that gives Latin 'rex' (king), 'regere' (to rule), and English
The 'royal prerogative' in British constitutional law refers to powers that the monarch can exercise without Parliamentary approval. The term preserves the original Roman sense perfectly: just as the 'praerogātīva centuria' had the right to vote before everyone else, the monarch has the right to act before (and without) Parliament. Being asked first meant having the most influence