Etymology
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undesirable (adj.)
1660s, "not to be desired, objectionable," from un- (1) "not" + desirable. The noun meaning "undesirable person or thing" is first attested 1883. Undesired "not asked or invited" is recorded from late 15c.
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exempt (v.)

c. 1400, exempten, "to relieve, to free or permit to be free" (from some requirement or condition, usually undesirable), from Anglo-French exempter, from exempt (adj.); see exempt (adj.). Related: Exempted; exempting.

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forebode (v.)
"feel a secret premonition," especially of something evil, c. 1600, from fore- + bode. Transitive meaning "announce beforehand, presage," especially something undesirable, is from 1660s. Intransitive sense "to presage" is from 1711. Related: Foreboded; foreboding. Old English forebodian meant "to announce, declare."
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liable (adj.)

mid-15c., "bound or obliged by law," probably from Anglo-French *liable, from Old French lier "to bind, tie up, fasten, tether; bind by obligation" (12c.), from Latin ligare "to bind, to tie" (from PIE root *leig- "to tie, bind"). With -able. Perhaps from an unattested word in Old French or Medieval Latin. General sense of "exposed to" (something undesirable) is from 1590s. Incorrect use for "likely" is attested by 1850.

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spiffy (adj.)
1853, of uncertain origin, probably related to spiff "well-dressed man." Uncertain relationship to spiff (n.) "percentage allowed by drapers to their young men when they effect sale of old fashioned or undesirable stock" (1859), or to spiflicate "confound, overcome completely," a cant word from 1749 that was "common in the 19th century" [OED], preserved in American English and yielded slang spiflicated "drunk," first recorded in that sense 1902.
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purge (n.)

1560s, "that which purges," from purge (v.). Meaning "a purgative, an act of purging" is from 1590s. Political or social sense of "removal (from a governing body, party, army, etc.) of persons deemed undesirable" is by 1730 (in reference to Pride's Purge); modern use in reference to the Soviet Union is by 1933. The earliest sense of the word in English was "examination or interrogation in a legal court" (mid-15c.), a sense now obsolete even if the feeling persists.

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incur (v.)
c. 1400, "bring (an undesirable consequence) upon oneself;" mid-15c. as "become liable for (payment or expenses)," from Anglo-French encurir, Old French encorir "to run, flee; commit, contract, incur" (Modern French encourir), from Latin incurrere "run into or against, rush at, make an attack;" figuratively, "to befall, happen, occur to," from in- "upon" (from PIE root *en "in") + currere "to run" (from PIE root *kers- "to run"). Related: Incurred; incurring.
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exemption (n.)

c. 1400, exempcioun, "immunity from a law or statute, state of being free from some undesirable requirement," from Old French exemption, exencion or directly from Latin exemptionem (nominative exemptio) "a taking out, removing," noun of action from past-participle stem of eximere "remove, take out, take away; free, release, deliver, make an exception of," from ex "out" (see ex-) + emere "buy," originally "take," from PIE root *em- "to take, distribute." 

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eliminate (v.)

1560s, "to thrust out, remove, throw out of doors," from Latin eliminatus, past participle of eliminare "thrust out of doors, expel," from ex limine "off the threshold," from ex "off, out" (see ex-) + limine, ablative of limen "threshold" (see limit (n.)).

Used literally at first; the sense of "exclude, throw aside, or disregard as undesirable or unnecessary" is attested by 1714; the sense of "expel waste from the body" is by c. 1795. Related: Eliminated; eliminating; eliminative; eliminatory.

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crud (n.)

U.S. slang; said in "Dictionary of American Slang" to be originally 1920s army and 1930s college student slang for "venereal disease." Thus by 1940, "dirty, disreputable person," and by 1950, "undesirable impurity." By 1945 (with various modifiers) it was the G.I.'s name for disease of any and every sort." 

Perhaps this word is a continuation of crud as the old metathesis variant of curd (q.v.), which would make it an unconscious return to the original Middle English form of that word. Century Dictionary (1897) has crud only in the sense "Obsolete or dialectal form of curd."

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