The word 'nice' is not a noun. The word 'nice' is an adjective, a word used to describe a noun. The adjective 'nice' can describe a singular or a plural noun.
Examples:
This is a nice apple.
These are nice apples.
The noun 'mice' is the plural form of the singular noun 'mouse'.
The noun 'circus' is a singular noun.The plural noun is 'circuses'.
The noun juggler is a singular noun. The plural noun is jugglers.
Statistics is plural, the singular form is statistic.
The word moon is a singular noun. The plural noun is moons.
The noun 'mice' is the plural form of the singular noun 'mouse'.
The singular noun is "louse" and the plural noun is "lice."
noun that are plural in form but singular in meaning
The noun children is the plural form of the singular noun child.
The noun 'circus' is a singular noun.The plural noun is 'circuses'.
The noun juggler is a singular noun. The plural noun is jugglers.
The noun 'orange' is a singular noun, a word for one piece of fruit, a word for one color. The plural noun is oranges.Examples:Mom put an orange in my lunch box. (singular)The pumpkins were a nice shade of orange. (singular, one shade)I took a photo of the bowl of oranges. (plural)
The singular noun is trio; the plural noun is trios.
The singular noun is Tuesday.The plural noun is Tuesdays.
The noun 'orchid' is a singular noun, a word for one.The plural noun is 'orchids'.
The noun mailbox is the singular form; the plural is mailboxes.
Statistics is plural, the singular form is statistic.