Ebony defines an obtuse angle as an angle that is not acute. Is Ebony's definition valid?

no because there are also right angles. an obtuse angle can best be defined as an angle greater than 90 degrees and less than 180 degrees

Ebony's definition is not valid.

Step-by-step explanation:

Obtuse angle is an angle that measures more than 90 degrees but less than 180 degrees.

And acute angles measure more than zero degrees and less than 90 degrees.

We know that a right triangle is neither acute nor obtuse.

As Ebony has not mentioned right angles, so her definition is not valid.