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Origin and history of irrational

irrational(adj.)

late 15c., "not endowed with reason" (of beasts, etc.), from Latin irrationalis/inrationalis "without reason, not rational," from assimilated form of in- "not, opposite of" (see in- (1)) + rationalis "of or belonging to reason, reasonable" (see rational (adj.)).

Meaning "illogical, absurd" is attested from 1640s. Related: Irrationally. The mathematical sense "inexpressible in ordinary numbers" is from late 14c. in English, from use of the Latin word as a translation of Greek alogon in Euclid.

also from late 15c.

Entries linking to irrational

rational(adj.)

late 14c., racional, "pertaining to or springing from reason;" mid-15c., of persons, "endowed with reason, having the power of reasoning," from Old French racionel and directly from Latin rationalis "of or belonging to reason, reasonable," from ratio (genitive rationis) "reckoning, calculation, reason" (see ratio).

In arithmetic, "expressible in finite terms," 1560s. Meaning "conformable to the precepts of practical reason" is from 1630s. Related: Rationally. It is from the same source as ratio and ration; the sense in rational is aligned with that in related reason (n.), which got deformed in French.

irrationality(n.)

1560s, originally in the mathematical sense, from irrational + -ity. Meaning "unreasonableness, absurdity" is from 1640s.

in-(1)

word-forming element meaning "not, opposite of, without" (also im-, il-, ir- by assimilation of -n- with following consonant, a tendency which began in later Latin), from Latin in- "not," cognate with Greek an-, Old English un-, all from PIE root *ne- "not."

In Old French and Middle English often en-, but most of these forms have not survived in Modern English, and the few that do (enemy, for instance) no longer are felt as negative. The rule of thumb in English has been to use in- with obviously Latin elements, un- with native or nativized ones.

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    insensate
    1510s, "lacking or deprived of physical senses," from Late Latin insensatus "irrational, foolish," from in- "not" (see in...Meaning "irrational, maniacal, lacking or deprived of mental sense" is from 1520s; meaning "lacking or deprived of moral...
    phobia
    "irrational fear, horror, or aversion; fear of an imaginary evil or undue fear of a real one," 1786, perhaps based on a similar...The psychological sense of "an abnormal or irrational fear" is attested by 1895....
    occultism
    Dodds, "The Greeks and the Irrational," 1951, footnote]...
    postal
    Noun meaning "state of irrational and violent anger" (usually in phrase going postal) is attested by 1997, in reference to...
    populism
    people who see their concerns as being disregarded by established parties and elites, but it also is used pejoratively for irrational...
    celebrity
    Dodds, "The Greeks and the Irrational"]...
    Mesopotamia
    In 19c. the word sometimes was used in the sense of "anything which gives irrational or inexplicable comfort to the hearer...
    earl
    Old English eorl "brave man, warrior, leader, chief" (contrasted with ceorl "churl"), from Proto-Germanic *erlaz, which is of uncertain origin. In Anglo-Saxon poetry, "a warrior, a brave man;" in later Old English, "nobleman," especially a Danish under-king (equivalent of cognate
    real
    early 14c., "actually existing, having physical existence (not imaginary);" mid-15c., "relating to things" (especially property), from Old French reel "real, actual," from Late Latin realis "actual," in Medieval Latin "belonging to the thing itself," from Latin res "property, goo
    number
    c. 1300, "sum, aggregate of a collection," from Anglo-French noumbre, Old French nombre and directly from Latin numerus "a number, quantity," from PIE root *nem- "assign, allot; take." The meaning "written symbol or figure of arithmetic value" is from late 14c. The meaning "singl

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