abbreviation of agriculture, attested from 1830s (in Secretary of Ag., etc.); by 1880s in reference to college courses, American English.
Entries linking to ag
agriculture n.
mid-15c., "tillage, cultivation of large areas of land to provide food," from Late Latin agricultura "cultivation of the land," a contraction of agri cultura "cultivation of land," from agri, genitive of ager "a field" (from PIE root *agro- "field") + cultura "cultivation" (see culture (n.)). In Old English, the idea could be expressed by eorðtilþ.
aggie n.1
"college student studying agriculture," by 1880, American English college slang, from ag, abbreviation of agriculture, + -ie.