If "contour" refers to the outline or shape of something:
* Straight: This is the most direct opposite, implying a lack of curves or bends.
* Flat: This emphasizes the absence of any raised or lowered areas.
* Uniform: This implies a consistent, unchanging shape.
* Plain: This suggests a simple, unadorned surface.
If "contour" refers to the lines on a map that show elevation:
* Level: This signifies an even surface with no changes in elevation.
* Horizontal: This emphasizes the absence of any upward or downward slopes.
If "contour" refers to the outline of a body part:
* Straight: This implies a lack of curves or definition.
* Flat: This suggests a smooth, undifferentiated surface.
The best antonym for "contour" will depend on the specific context in which it is being used.