The act of growing out or the process of protruding; an outgrowth or excrescence.
From Latin excressio, from excrescere (to grow out); the -ion suffix indicates an action or process, so this noun describes the action of growing excessively outward.
While 'excrescence' is the result (the bump), 'excression' is the process (the act of bumping out)—it's like the difference between 'growth' (the thing) and 'growing' (the process), showing how English can create both with different suffixes.
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