Etymology
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interrogate (v.)
late 15c., a back-formation from interrogation or else from Latin interrogatus, past participle of interrogare "to ask, question, inquire; interrogate judicially, cross-examine," from inter "between" (see inter-) + rogare "to ask, to question," apparently a figurative use of a PIE verb meaning literally "to stretch out (the hand)," from root *reg- "move in a straight line." The Old French word was interroger (14c.) which yielded English interroge (late 15c.), now obsolete. Related: Interrogated; interrogating.
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*reg- 

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."

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probe (v.)

1640s, originally figurative; "to search thoroughly, scrutinize, interrogate;" from probe (n.) and partly from Latin probare "show, demonstrate; test, inspect." Physical sense of "to examine with a probe" is from 1680s. Related: Probed; probing; probingly.

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question (v.)

late 15c., questiounen, "to inquire, ask, seek to know," from question (n.) and from Old French questioner "ask questions, interrogate, torture" (13c.), from question (n.). Hence "to dispute, doubt," by 1530s. Transitive sense of "inquire of by asking questions" is from late 15c. Related: Questioned; questioning. Alternative verb questionize is attested from 1847.

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interrogatory (adj.)
"containing or expressing a question," 1570s, from Late Latin interrogatorius "consisting of questions," from past participle stem of Latin interrogare "to ask, question, inquire; interrogate judicially, cross-examine," from inter "between" (see inter-) + rogare "to ask, to question," apparently a figurative use of a PIE verb meaning literally "to stretch out (the hand)," from root *reg- "move in a straight line."
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pose (v.2)

"to puzzle, confuse, perplex," 1590s, earlier "to put questions to, interrogate closely" (1520s), probably from French poser "suppose, assume," from Old French poser "to put, place, set" (see pose (v.1)). Also in some cases a shortening of English appose "examine closely," and directly from oppose (of which appose was a variant). Related: Posed; posing.

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interrogation (n.)
late 14c., "a question;" c. 1500, "a questioning; a set of questions," from Old French interrogacion "a questioning" (13c.) or directly from Latin interrogationem (nominative interrogatio) "a question; questioning; judicial inquiry," noun of action from past participle stem of interrogare "to ask, question, inquire; interrogate judicially, cross-examine," from inter "between" (see inter-) + rogare "to ask, to question," apparently a figurative use of a PIE verb meaning literally "to stretch out (the hand)," from root *reg- "move in a straight line."
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interrogative (adj.)
"asking or denoting a question," c. 1500, from Late Latin interrogativus "pertaining to a question," from interrogat-, past participle stem of Latin interrogare "to ask, question, inquire; interrogate judicially, cross-examine," from inter "between" (see inter-) + rogare "to ask, to question," apparently a figurative use of a PIE verb meaning literally "to stretch out (the hand)," from root *reg- "move in a straight line." As a noun, "word implying a question," 1520s. Related: Interrogatively.
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oppose (v.)

late 14c., opposen, "to speak or act against; accuse, question, interrogate," from Old French oposer "oppose, resist, rival; contradict, state opposing point of view" (12c.), apparently from assimilated form of Latin ob- "in the direction of, in front of" (see ob-) + French poser "to place, lay down" (see pose (v.1)), with the sense blended with that of Latin opponere "oppose, object to, set against" (see opponent). The meaning "to set or place over against or directly opposite" (transitive) and "interpose effort or objection, be adverse, act adversely" (intransitive) are from 1590s. Related: Opposed; opposing.

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examine (v.)

c. 1300, "put (someone) to question in regard to knowledge, competence, or skill, inquire into qualifications or capabilities;" mid-14c., "inspect or survey (something) carefully, scrutinize, view or observe in all aspects with the purpose of forming a correct opinion or judgment," from Old French examiner "interrogate, question, torture," from Latin examinare "to test or try; consider, ponder," literally "to weigh," from examen "a means of weighing or testing," probably ultimately from exigere "demand, require, enforce," literally "to drive or force out," also "to finish, measure," from ex "out" (see ex-) + agere "to set in motion, drive, drive forward; to do, perform" (from PIE root *ag- "to drive, draw out or forth, move"). Legal sense of "question or hear (a witness in court)" is from early 15c. Related: Examined; examining.

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