This could appear more efficiently as: His critics both over- and underestimated his abilities. In this role, the hyphen is called a suspension hyphen. A suspension hyphen informs the reader that there is something intentionally missing; that over is not intended as a complete word in itself but just as the first part of a compound, the remainder of which is about to be identified. It is important to include the hyphen, for omitting it would create momentary confusion as the reader tried to make sense of His critics both over and . (Note that use of the suspension hyphen is unrelated to whether or not the word it is standing in for is normally hyphenated.