gradation (
http://definr.com/gradation)
n 1: relative position in a graded series: "always a step
behind"; "subtle gradations in color"; "keep in step
with the fashions" [syn:
step]
2: a vowel whose quality or length is changed to indicate
linguistic distinctions (such as sing sang sung song)
[syn:
ablaut]
3: the act of arranging in grades [syn:
graduation]