10 letters · 15 points in Scrabble
adjective of an obscure nature; ; ; ; - Rachel Carson
adjective having an import not apparent to the senses nor obvious to the intelligence; beyond ordinary understanding
originFrom Middle English *misterius (implied in misteriusly), probably partly from Middle French mystérieux and partly from Latin mystērium + -ous. By surface analysis, mystery + -ous.
Etymology from Wiktionary, CC BY-SA 3.0