Septentrional is a word that means "of the north", rarely used in English but commonly used in French. Early maps of North America, mostly those before 1700, often refer to the northern- or northwestern-most unexplored areas of the continent at "Septentrional" or "America Septentrionalis", sometimes with slightly alternate spellings. The term septentrional, actually the adjectival form of the noun septentrion, itself refers to the seven stars of the Big Dipper asterism (aka "Septentrion").
The OED gives the etymology as
Gene Wolfe used the word in The Book of the New Sun as part of the name of a palace guard. Voltaire used this word in Candide (chapter 11). He used the plural form septentrionaux. It only appears in the French version. In the English version, the word is translated to "northern".
The term, sometimes abbreviated to "Sep.", was used in historical astronomy to indicate the northern direction on the celestial globe, together with Meridional ("Mer.") for southern, Oriental ("Ori.") for eastern and Occidental ("Occ.") for western.