grade (n.)youdaoicibaDictYouDict[grade 词源字典]
1510s, "degree of measurement," from French grade "grade, degree" (16c.), from Latin gradus "step, pace, gait, walk; step on a ladder or stair;" figuratively "a step, stage, degree," from gradi (past participle gressus) "to walk, step, go," from PIE *ghredh- "to walk, go" (cognates: Lithuanian gridiju "to go, wander," Old Church Slavonic gredo "to come," Old Irish in-greinn "he pursues," and second element in congress, progress, etc.). Replaced Middle English gree "step, degree in a series," from Old French grei "step," from Latin gradus.

Meaning "inclination of a road or railroad" is from 1811. Meaning "class of things having the same quality or value" is from 1807; meaning "division of a school curriculum equivalent to one year" is from 1835; that of "letter-mark indicating assessment of a student's work" is from 1886 (earlier used of numerical grades). Grade A "top quality, fit for human consumption" (originally of milk) is from a U.S. system instituted in 1912. To figuratively make the grade "be successful" is from 1912; early examples do not make clear whether the literal grade in mind was one of elevation, quality, or scholarship.[grade etymology, grade origin, 英语词源]
grade (v.)youdaoicibaDictYouDict
1650s, "to arrange in grades," from grade (n.). Meaning "to reduce (a road, etc.) to a level or degree of inclination" is from 1835. Meaning "assign a letter mark to" is from 1931. Related: Graded; grading.