The word 'outside' is an uncountable noun; a word for the aspect of something (The outside is shabby.)
The word outside is also:
The noun 'mice' is the plural form of the singular noun 'mouse'.
"Children" is a plural noun. The singular form is "child."
The noun 'circus' is a singular noun.The plural noun is 'circuses'.
The noun 'loss' is the singular noun. The plural noun is losses.
The noun juggler is a singular noun. The plural noun is jugglers.
The singular noun is Tuesday.The plural noun is Tuesdays.
The singular noun is trio; the plural noun is trios.
The noun 'orchid' is a singular noun, a word for one.The plural noun is 'orchids'.
Statistics is plural, the singular form is statistic.
No, Mice is a plural noun. Mouse is the singular noun.
The word aisle is a singular noun. The plural noun is aisles.
The noun 'days' is the plural form of the singular noun 'day'.