bon·chi /bon - chi /–noun, plural -s -Slang1. a lady whom shops at Bon Marche (bon) or any other middle level department store (Macy's) and tends to make a chirping (chi) noise when laughing or chatting with a small grouping of buddies.2. your message is a portmanteau: a blend of two (or even more) terms or morphemes and their definitions into one brand new term. Bon Marche + Chirp = bonchi-adjective3. typical of or showing the feature of a bonchi.