The act or state of making calm; the condition of being calmed.
From 'becalm' plus the suffix '-ment' (forming nouns of action or state), a now-archaic nominalization that was more common in Middle English.
Words ending in '-ment' were especially productive in Middle English for turning verbs into abstract nouns, but 'becalmment' barely survived into modern English—most people just say 'calm' or 'calmness' instead.
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