level

{{11}}level (adj.) early 15c., from LEVEL (Cf. level) (n.). To do one's level best is from 1851.

{{12}}level (n.) mid-14c., "tool to indicate a horizontal line," from O.Fr. livel "a level" (13c.), ultimately from L. libella "a balance, level," dim. of libra "balance, scale, unit of weight," from PIE *lithra. Cognate Sp. nivel, Mod.Fr. niveau are from the same source but altered by dissimilation. Meaning "horizontality" is from c.1400. Meaning "position as marked by a horizontal line" is from 1530s. Phrase on the level "fair, honest" is from 1872; earlier it meant "moderate, without great ambition" (1790).

{{12}}level (v.) mid-15c., "to make level," from LEVEL (Cf. level) (n.). From c.1600 as "to bring to a level;" 1958 as "to cease increasing." Meaning "to aim a gun" is late 15c. Slang sense of "tell the truth" is from 1920. To level up "to rise" is attested by 1863.

A word here as to the misconception labored under by our English neighbor; he evidently does not understand the American manner of doing things. We never level down in this country; we are always at work on the up grade. "Level up! Level up!" is the motto of the American people. [James E. Garretson, "Professional Education," in "The Dental Cosmos," Philadelphia, 1865]

To level off "cease rising or falling" is from 1920, originally in aviation.