The act or process of amassing; the gathering or accumulation of something in quantity.
From the verb amass with the suffix -ment (from Old French and Latin -mentum, indicating an act, process, or resulting state). This creates an abstract noun describing the action itself rather than its agent.
The -ment suffix turns verbs into abstract nouns—amazement, government, basement—and it's so old that it comes from Latin, showing how English borrowed structure-building tools from Romance languages.
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