Something that makes something else deeper or more profound; a thing or person that deepens understanding or a physical situation.
From 'deepen' (make deep) plus the suffix '-er' (one that does). The word emerged to describe both physical deepening (like a dredging tool) and metaphorical deepening (like insight).
A deepener could be a literal dredging machine or a metaphorical concept that adds layers to your understanding—the word's flexibility shows how English can use the same word formation for both physical and mental operations.
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