idempotent (n.)

"the same (as above)," used to avoid repetition in writing, Latin, literally "the same," from id "it, that one," from PIE pronominal stem *i- (see yon) + demonstrative suffix -dem.

early 15c., "mighty, very powerful, possessed of inherent strength," from Latin potentem (nominative potens) "powerful," present participle of posse "be able, be powerful," a contraction of potis esse "be powerful, be master," from potis "powerful, able, capable; possible;" of persons, "better, preferable; chief, principal; strongest, foremost," from PIE root *poti- "powerful; lord." "The exact process leading from potis + esse to the paradigm of posse is disputed" [de Vaan].

The meaning "having sexual power, capable of orgasm in sexual intercourse" (of men) is recorded by 1893.

posse "be able, be powerful," a contraction of potis esse "be powerful, be master,"

Proto-Indo-European root meaning "powerful; lord." 

It forms all or part of: bashaw; compos mentis; despot; hospodar; host (n.1) "person who receives guests;" idempotent; impotent; omnipotent; pasha; plenipotentiary; posse; possess; possible; potence; potency; potent; potentate; potential; potentiate; potentiometer; power; totipotent. 

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit patih "master, husband;" Greek posis, Lithuanian patis "husband;" Latin potis "powerful, able, capable; possible."