gradual
adj.
early 15c., "having steps or ridges," from Medieval Latin gradualis, from Latin gradus "step" (see grade, n.). Meaning "arranged by degrees" is from 1540s; that of "taking place by degrees" is from 1690s.
〔蒋〕[grad步，-ual形容词后缀，…的] 逐步的，逐渐的
〔李〕[grad=step步；-u-;-al a.=of……的→“of steps一步步的”→] a. step by step逐步的