Dosage

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late Middle English: from French, via late Latin from Greek dosis ‘gift’, from didonai ‘give’.

wiktionary

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From French dosage.

etymonline

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dosage (n.)

1867 in chemistry; 1874 in medicine, "act or practice of administering medication in doses," especially in reference to the size; see dose + -age, perhaps on model of French dosage (1812).