What's the difference between i.e. and e.g.?
early 15c., from Late Latin incentivum, noun use of neuter of Latin adjective incentivus "setting the tune" (in Late Latin "inciting"), from past participle stem of incinere "strike up," from in- "in, into" (see in- (2)) + canere "sing" (see chant (v.)). Sense influenced by association with incendere "to kindle." The adjective use, in reference to a system of rewards meant to encourage harder work, first attested 1943 in jargon of the U.S. war economy; as a noun, in this sense, from 1948.