The act or process of embarking; boarding a vessel or aircraft.
From embark + suffix '-ment' (forming nouns from verbs, indicating an action, process, or result). The '-ment' suffix comes from Old French and Latin and is extremely productive in English.
Embarkment and embarkation mean nearly the same thing, but 'embarkment' is much rarer today—it's a great example of how English can have competing word formations, and some eventually 'win' and others fade away as language evolves.
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