There are a few adjectives in Spanish which have a shortened masculine, singular form when used before a noun. This is often indicates slightly different meanings, which can vary widely depending on the culture. For instance, the difference between un chico malo (a mean child) and un mal chico (a bad child) is generally a matter of severity.

Most of these adjectives are rooted in the difference between uno (one) and un (a). That is, they stress the final syllable and drop the -o ending, while taking on an de-emphasized role.

One word that is in the list but shouldn't be is según, which historically was a shortened form of "second", but has since lost that use, while primer (first) and tercer (third) have retained it. Today it is used as a preposition meaning "according to".