book word

noun2

1. •
   A word that is encountered in writing but not usually in speech, which people may therefore not know how to pronounce (correctly).

   • The second, being a ‘book word,’ has quite an artificial pronunciation. — 1871
2. •
   A word that is borrowed into a vernacular from a closely related literary language, thus being etymologically related to native vocabulary, but not showing regular sound changes.

   • French loyal and légal are both from Latin lēgālis. While the former was inherited, the latter is a book word.