Flattest

adjective

1. Having no variations in height.

   "The land around here is flat."

2. (voice) Without variations in pitch.
3. Having small or invisible breasts and/or buttocks.

   "That girl is completely flat on both sides."

4. (note) Lowered by one semitone.
5. Of a note or voice, lower in pitch than it should be.

   "Your A string is too flat."