His voice, deep and full for so young a child, inclined to unflattened vowels.
Their distance from the centre, compared with the radius of the unflattened circle, is called the excentricity.
late 14c., "to prostrate oneself," also "to fall flat," from flat (adj.) + -en (1). Meaning "to make flat" is 1620s. Related: Flattened; flattening.