flat

Having no variations in height.

In a horizontal line or plane; not sloping.

Smooth; having no protrusions, indentations or other surface irregularities, or relatively so.

Having small or invisible breasts and/or buttocks.

Without variation in level, quantity, value, tone etc.

At a consistently depressed level; consistently lacklustre.

Of fees, fares etc., fixed; unvarying.

Without variations in pitch.

Not diphthongal; without variation in height or backness.

Without variation in tone or hue (uniform), and dull (not glossy).