illegitimate (adj.)

1530s, "born out of wedlock," formed in English (and replacing earlier illegitime, c. 1500), modeled on Late Latin illegitimus "not legitimate" (see il- + legitimate). Sense of "unauthorized, unwarranted" is from 1640s. Phrase illegitimi non carborundum, usually "translated" as "don't let the bastards grind you down," is fake Latin (by 1965, said to date from c. 1939). Carborundum was a brand of abrasives. Related: Illegitimately.

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Definitions of illegitimate from WordNet
illegitimate (adj.)
contrary to or forbidden by law;
an illegitimate seizure of power
Synonyms: illicit / outlaw / outlawed / unlawful
illegitimate (adj.)
of marriages and offspring; not recognized as lawful;
illegitimate (n.)
the illegitimate offspring of unmarried parents;
Synonyms: bastard / by-blow / love child / illegitimate child / whoreson