FLATCAP Meaning of FLATCAP in English ˈ ̷ ̷ˌ ̷ ̷ noun 1. : a round low-crowned cap worn in 16th and 17th century England especially in London2. : a wearer of a flatcap ; especially : londoner Webster's New International English Dictionary. Новый международный словарь английского языка Webster. 2012