as a noun, 'small' refers to something that is of a smaller size, especially in relation to clothing sizes.
I'll take a small in that shirt.
The smalls are on the top shelf.
Do you have this in a small?
When 'small' is used as a noun in the context of clothing, it's often in contrast to other sizes like medium, large, etc.
as an adjective, 'small' describes the size of something, indicating that it is of limited size or is lesser in size than others of its kind.
She lives in a small apartment.
There's only a small chance of rain today.
He made a small error in his calculations.
'Small' can be used in comparative and superlative forms that are 'smaller' and 'smallest.'
s an adverb, 'small' is used less frequently and typically in set phrases. It can describe an action done to a limited degree.
He smiled, small.
She nodded small in agreement.
The adverbial use of 'small' is less common and might sound archaic or poetic in some contexts.