英语词源字典 - 在线词源网站

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]
regression (n.): early 15c., from Latin regressionem (nominative regressio) "a going back, a return," noun of action from past participle stem of regredi (see regress (n.)).