imperator n.

1520s, in grammar, "expressing command," used of the form of a verb which expresses command, entreaty, advice, or exhortation, from Late Latin imperativus "pertaining to a command," from imperat-, past participle stem of imperare "to command, requisition," from assimilated form of in- "into, in" (from PIE root *en "in") + parare "to arrange, prepare, adorn" (from PIE root *pere- (1) "to produce, procure").

*perə-, Proto-Indo-European root meaning "to produce, procure" and yielding and derived words in diverse senses; possibly related to *pere- (2) "to grant, allot."

It forms all or part of: ante-partum; apparatus; apparel; biparous; disparate; emperor; empire; heifer; imperative; imperator; imperial; juniper; multiparous; nulliparous; oviparous; para- (2) "defense, protection against; that which protects from;" Parabellum; parachute; parade; parados; parapet; parasol; pare; parent; -parous; parry; parturient; poor; post-partum; preparation; prepare; primipara; puerperal; rampart; repair (v.1) "to mend, put back in order;" repertory; separate; sever; several; spar (v.); viper; vituperation; viviparous.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit prthukah "child, calf, young of an animal;" Greek poris "calf, bull;" Latin parare "make ready, prepare," parire "produce, bring forth, give birth to;" Czech spratek "brat, urchin, premature calf;" Lithuanian periu, perėti "to brood;" Old High German farro, German Farre "bullock," Old English fearr "bull."