late 14c., "upright, not bending," from Latin erectus "upright, elevated, lofty; eager, alert, aroused; resolute; arrogant," past participle of erigere "raise or set up," from e- "up, out of" + regere "to direct, keep straight, guide" (from PIE root *reg- "move in a straight line," with derivatives meaning "to direct in a straight line," thus "to lead, rule").

c. 1400, a back-formation from erect (adj.) or else from Latin erectus. Related: Erected; erecting.

1822, "pertaining to muscular erection," from French érectile, from Latin erect-, past participle stem of erigere "to raise or set up" (see erect (adj.)).

"capable of being erected," 1785, from stem of Latin erigere "to raise or set up" (see erect (adj.)).

1530s, "one who builds," agent noun in Latin form from erect (v.). In reference to muscles from 1831. The children's building kit Erector (commonly known as an Erector set) was sold from 1913.

mid-15c., "establishment; advancement," from Late Latin erectionem (nominative erectio), noun of action from past participle stem of erigere "to set up, erect" (see erect (adj.)). Meanings "the putting up" (of a building, etc.), "stiffening of the penis" (also sometimes of the turgidity and rigidity of the clitoris) are both from 1590s.

"on the watch," 1610s, from French alerte "vigilant" (17c.), from prepositional phrase à l'erte "on the watch," from Italian all'erta "to the height." The second element is from erta "lookout, high tower," noun use of fem. of erto, past participle of ergere "raise up," from Latin erigere "raise" (see erect (adj.)).

The adjective is attested from 1712; the noun is from 1796 as "attitude of vigilance" (as in on the alert); 1803 as "a warning report." The verb is by 1864. Related: Alerted; alerting.

Proto-Indo-European root meaning "move in a straight line," with derivatives meaning "to direct in a straight line," thus "to lead, rule."

It forms all or part of: abrogate; address; adroit; Alaric; alert; anorectic; anorexia; arrogant; arrogate; bishopric; correct; corvee; derecho; derogate; derogatory; Dietrich; direct; dress; eldritch; erect; ergo; Eric; Frederick; Henry; incorrigible; interregnum; interrogate; maharajah; Maratha; prerogative; prorogue; rack (n.1) "frame with bars;" rail (n.1) "horizontal bar passing from one post or support to another;" Raj; rajah; rake (n.1) "toothed tool for drawing or scraping things together;" rake (n.2) "debauchee; idle, dissolute person;" rakish; rank (adj.) "corrupt, loathsome, foul;" real (n.) "small Spanish silver coin;" realm; reck; reckless; reckon; rectangle; rectify; rectilinear; rectitude; recto; recto-; rector; rectum; regal; regent; regicide; regime; regimen; regiment; region; regular; regulate; Regulus; Reich; reign; resurgent; rex; rich; right; Risorgimento; rogation; royal; rule; sord; source; subrogate; subrogation; surge; surrogate; viceroy.

It is the hypothetical source of/evidence for its existence is provided by:

Sanskrit raj- "a king, a leader," rjyati "he stretches himself," riag "torture" (by racking); Avestan razeyeiti "directs," raštva- "directed, arranged, straight;" Persian rahst "right, correct;" Latin regere "to rule, direct, lead, govern," rex (genitive regis) "king," rectus "right, correct;" Greek oregein "to reach, extend;" Old Irish ri, Gaelic righ "a king," Gaulish -rix "a king" (in personal names, such as Vircingetorix), Old Irish rigim "to stretch out;" Gothic reiks "a leader," raihts "straight, right;" Lithuanian raižytis "to stretch oneself;" Old English rice "kingdom," -ric "king," rice "rich, powerful," riht "correct;" Gothic raihts, Old High German recht, Old Swedish reht, Old Norse rettr "correct."

1610s, "an image of the penis," from Latin phallus, from Greek phallos "penis," also "carving or image of an erect penis (symbolizing the generative power in nature) used in the cult of Dionysus," from PIE *bhel-no-, from root *bhel- (2) "to blow, swell" (source also of Old Norse boli "bull," Old English bulluc "little bull," and possibly Greek phalle "whale"). Used of the penis itself (especially if erect, but often in symbolic context) by 1891 (Hargrave Jennings).