Initiation

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mid 16th century (in initiate (sense 2 of the verb)): from Latin initiat- ‘begun’, from the verb initiare, from initium ‘beginning’.

wiktionary

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Borrowed from Middle French initiation, from Latin initiātiō. Morphologically initiate +‎ -ion

etymonline

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initiation (n.)

1580s, from French initiation or directly from Latin initiationem (nominative initiatio) "participation in secret rites," noun of action from past-participle stem of initiare "originate, initiate," from initium "a beginning" (see initial (adj.)).