* Adjective: This is the most common usage. It describes a noun, like "a small dog" or "a small problem."
* Noun: Less common, but "small" can be a noun referring to something small, like "the smalls" (referring to children's clothes).
* Adverb: In rare cases, "small" can act as an adverb meaning "to a small degree," like "He smiled small" (meaning he smiled subtly).
To determine the correct part of speech, you need to look at how the word is used in the specific sentence.