degression (n.)

"a stepping down, descent" (obsolete), 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-) + gradi "to walk, go, step" (from PIE root *ghredh- "to walk, go").