c. 1300, "sweet smell, scent, fragrance," from Anglo-French odour, from Old French odor "smell, perfume, fragrance" (12c., Modern French odeur) and directly from Latin odor "a smell, a scent" (pleasant or disagreeable), from PIE root *hed- "to smell" (source also of Latin olere "emit a smell, to smell of," with Sabine -l- for -d-; Greek ozein "to smell," odme "odor, scent;" Armenian hotim "I smell;" Lithuanian uodžiu, uosti "to smell, sniff;" Old Czech jadati "to investigate, explore").
Neutral sense of "smell as an inherent property of matter; scent or fragrance whether pleasant or not" is from late 14c. "[W]hen used without a qualifying adjunct, the word usually denotes an agreeable smell" [Century Dictionary, 1895]. Good or bad odor, in reference to repute or esteem, is from 1835. Odor of sanctity (1756) is from French odeur de sainteté (17c.) "sweet or balsamic scent said to be exhaled by the bodies of eminent saints at death or upon disinterment." In Middle English odor also had a figurative sense of "spiritual fragrance of Christ's sacrifice."