Do you know ghouls from goblins and ghosts?
late 13c., "inherently, intrinsically, characteristically," from natural + -ly (2). From late 14c. as "in accord with natural law;" also "normally; usually, expectedly; as a matter of course, consequently, understandably." The notion is "as a natural result." From early 15c. as "without artificial assistance, by a natural process."