The term 'pertaining to a sovereign' can be expressed by two words: regnal and ROYAL. Regnal is a six-letter word derived from the Latin regnum, meaning kingdom or realm. It is used to describe something that relates to a monarch or ruler. ROYAL, on the other hand, is a five-letter word derived from the Latin regalis, meaning of or belonging to a king or queen. It is used to describe something that is associated with a monarchy or royalty. Both words are used to describe something that is related to a sovereign.