(n)beginning, origin, root, rootage, sourcethe place where something begins, where it springs into being“the Italian beginning of the Renaissance”, “Jupiter was the origin of the radiation”, “Pittsburgh is the source of the Ohio River”, “communism's Russian root”
(n)reservoir, sourceanything (a person or animal or plant or substance) in which an infectious agent normally lives and multiplies“an infectious agent depends on a reservoir for its survival”
(n)reference, sourcea publication (or a passage from a publication) that is referred to“he carried an armful of references back to his desk”, “he spent hours looking for the source of that quotation”