Accusation

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late Middle English: from Old French, from Latin accusatio(n- ), from accusare ‘call to account’ (see accuse).

wiktionary

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First attested in the late 14th century. From Middle English accusacion, borrowed from Old French acusacion (French accusation), from Latin accūsātiō(“accusation, indictment”), from accūsō(“blame, accuse”). Doublet of accusatio. More at accuse. Equivalent to accuse +‎ -ation

etymonline

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accusation (n.)

late 14c., "charge of wrongdoing," from Old French acusacion "charge, indictment" (Modern French accusation) or directly from Latin accusationem (nominative accusatio) "formal complaint, indictment," noun of action from past-participle stem of accusare "call to account, make complaint against," from ad causa, from ad "with regard to" (see ad-) + causa "a cause; a lawsuit" (see cause (n.)). Meaning "that which is charged (against someone)" is from early 15c.