Suffix that can change an adjective to a noun?

There are a few suffixes that can change an adjective into a noun, but the most common one is -ness.

Here are some examples:

* Happy (adjective) -> Happiness (noun)

* Sad (adjective) -> Sadness (noun)

* Kind (adjective) -> Kindness (noun)

* Dark (adjective) -> Darkness (noun)

Other suffixes that can be used, though less common, include:

* -ity: Beautiful (adjective) -> Beauty (noun)

* -ty: Angry (adjective) -> Anger (noun)

* -th: Strong (adjective) -> Strength (noun)

* -hood: Child (adjective) -> Childhood (noun)

Keep in mind that not all adjectives can be turned into nouns using these suffixes. The choice of suffix depends on the specific adjective and the desired meaning.