The oracle bone form of 宀 is a pictograph depicting a wooden roof with supports. It is a part of a set of radicals (冖,宀 and 穴) collectively refered to as 宝盖头 (bǎo ɡài tóu) or "protection radicals". Each radical in this set references a protective covering. 宀 is called 宝盖头 (bǎo ɡài tóu) as opposed to 秃宝盖头 (tū bǎo ɡài tóu) for 冖 or 穴宝盖头 (xué bǎo ɡài tóu) for 穴, because it is the original "protection radical".
宀 is a very common radical, radical number 40, found in many housing-related words such as: 家 (Jiā) "home"，安 (ān) "safe, secure, peaceful", 宗 (zōng) "ancestor, clan"; as well as many other words like: 字 (zì) "letter, character, word", 宝 (bǎo) "treasure", and 客 (kè) "guest".