IPA: /ˈbæŋkˌroʊlər/
KK: /ˈbæŋkˌroʊlər/
A person or organization that provides financial support or funding for a project, business, or individual.
The film was made possible thanks to a generous bankroller who believed in the project.
Bankroller is formed from "bank" (from Old Italian *banca*, meaning a bench or table for money exchange) and "-roller" (from the verb "to roll", meaning to cause to move in a circular course). The term refers to someone who provides financial support, essentially rolling out money for a project or venture.
Think of a 'bank' as a place where money is kept and 'roller' as someone who helps to 'move' or provide that money. This helps you remember that a bankroller is someone who supports financially.
No commonly confused words.