c. 1300, erbe "non-woody plant," especially a leafy vegetable used for human food, from Old French erbe "grass, herb, plant fed to animals" (12c., Modern French herbe), from Latin herba "grass, an herb; herbage, turf, weeds" (source also of Spanish yerba, Portuguese herva, Italian erba). The form of the English word was refashioned after Latin since 15c., but the h- was mute until 19c. Slang meaning "marijuana" is attested from 1960s. The native word is wort.
1610s, from Latin herbalis, from herba "grass, herb" (see herb). Earlier as a noun, "book that names and classifies plants" (1510s).
c. 1300, herber, "herb garden, pleasure garden," from Old French erbier "field, meadow; kitchen garden," from Latin herba "grass, herb" (see herb). Later "a grassy plot" (mid-14c., a sense also in Old French), "shaded nook, bower formed by intertwining of trees, shrubs, or vines" (mid-14c.). It is probably not from Latin arbor "tree" (see arbor (n.2)), though perhaps that word has influenced its spelling:
[O]riginally signifying a place for the cultivation of herbs, a pleasure-ground, garden, subsequently applied to the bower or rustic shelter which commonly occupied the most conspicuous situation in the garden ; and thus the etymological reference to herbs being no longer apparent, the spelling was probably accommodated to the notion of being sheltered by trees or shrubs (arbor). [Hensleigh Wedgwood, "A Dictionary of English Etymology," 1859]