IPA: /ˈbɪlˌfoʊld/
KK: /ˈbɪlˌfoʊld/
A small, foldable case used to hold paper money, cards, and personal documents.
He took out his billfold to pay for the groceries.
Billfold is formed from "bill" (from Old English *billa*, meaning a document or note) and "fold" (from Old English *faldan*, meaning to fold). The word refers to a folded item used to hold bills or documents.
Think of a 'document' ('bill') that is 'folded' ('fold') to keep it organized — that's what a billfold is.