means A person or organization that provides financial or other support for someone or something, usually in exchange for advertising or in expectation of a return.

from Straight from Latin *spondere*, "to promise solemnly, to pledge" — the same root that gives us "spouse" (one pledged) and "respond" (to pledge in return). A *sponsor* in Roman and early Christian use was literally a guarantor: the one who stood up and vowed on your behalf, especially the godparent at a baptism. The word kept that flavor of "someone who answers for you" before drifting, by the 20th century, toward the one who pays — first for radio and television programs — and answers for the bill instead of your soul.