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degression (n.)[degression 词源字典]: late 15c., from Latin degressionem (nominative degressio) "a going down," noun of action from past participle stem of degredi "to go down, march down, descend," from de- "down" (see de-) + gradus "step" (see grade (n.)).[degression etymology, degression origin, 英语词源]