The prefixes over- and under- —meaning, respectively, (1) too or (2) above, and (1) insufficiently or (2) beneath—may be attached to virtually any adjective or verb without a hyphen. Your spell-check may urge you not to use words like underintelligent, overlove, undermarket, overroof, underfoundation, and oversunny, but these are perfectly good coinages requiring no hyphen. Spell-check is not infallible.
Examples
Although the over- and under- prefixes can be attached hyphenlessly to almost any adjective or verb, many writers and editors are timid about doing so—for example:
Parents tend to over-treat fevers, even waking up sleeping kids to give them fever-reducing medicine … [CBS News]
Roth explained that the legislature first began to under-fund the program back in 1993. [KSAL]
Personally, I think times in the 40-yard dash are mildly over-rated. [The Virginia-Pilot]
Most of our kids are under-skilled. [Stuff.co.nz]
But there’s no reason why these hyphenated phrases should not be condensed into single words—for example:
The report, published today in the online journal Pediatrics, says parents tend to overtreat fevers. [The Detroit News]
It would underfund school districts by 11 percent, or $231 million. [Bloomberg]
It believes the evidence of its eyes, not word-play from dodgy politicians and underskilled public relations flacks. [Courier Mail]
