Relating to or characterized by depression, or concerning an area of land that is sunken or lower than surrounding areas.
From depression + '-al' (adjective suffix meaning 'relating to'). In geology, it specifically describes topographic features that are recessed.
A depressional area in a swamp holds water—and 'depression' in psychology literally comes from the Latin idea of being 'pressed down,' so the words are metaphorically identical even in different fields.
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