A sponsor provides support for someone or something, typically by supplying cash. Because your company is a sponsor for a homeless organization, they provide funding for the annual 5K run to raise money for the shelter.
The word sponsor stems from the Latin word spondre, meaning "give assurance, promise solemnly." A sponsor might support an important issue such as cancer research or education, or a sponsor might take responsibility for someone. You might be your brother's sponsor so he can join your exclusive chess group. Sponsor has a verb form to describe the action of supporting or leading something. You can sponsor a nonprofit arts organization by donating and participating on the board.