Page "Opposite (semantics)" Paragraph 5

Other words are opposable but have an accidental gap in a given language's lexicon.

For example, the word devout lacks a lexical opposite, but it is fairly easy to conceptualize a parameter of devoutness where devout lies at the positive pole with a missing member at the negative pole.

Opposites of such words can nevertheless sometimes be formed with the prefixes un-or non -, with varying degrees of naturalness.

For example, the word undevout appears in Webster's dictionary of 1828, while the pattern of non-person could conceivably be extended to non-platypus.

Conversely, some words appear to be a prefixed form of an opposite, but the opposite term does not exist, such as inept, which appears to be in-+ * ept ; such a word is known as an unpaired word.