illegitimacy (n.)

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.

word-forming element making nouns of quality, state, or condition, a confusion in English of three similar suffixes from Latin:

1. in primacy, etc., from Old French -acie and directly from Medieval Latin -acia, Late Latin -atia, making nouns of quality, state, or condition from nouns in -as.

2. in advocacy, etc., from Late Latin -atia, forming nouns of state from nouns in -atus.

3. in fallacy, etc., from Latin -acia, forming nouns of quality from adjectives in -ax (genitive -acis). Also forming part of -cracy. It has been extended in English to nouns not found in Latin (accuracy) and to non-Latin words (piracy).