Singular. The plural would be "superstitions".
Example:
A superstition says that breaking a mirror brings a person seven years of bad luck.
She doesn't believe in silly superstitions.
No the word notes is a plural noun. The singular noun is note.
The noun 'loss' is the singular noun. The plural noun is losses.
The word army is a singular noun; armies is the plural form.
The word 'antelope' is a singular noun, a word for one animal.The plural noun is 'antelopes'.
The noun 'scales' is a plural noun, a word form two or more.The singular noun is 'scale'.
The noun personalities is the plural form for the singular noun personality.
The word clotheslines is a plural noun. The singular noun is clothesline.
The word temperature is a singular noun. The plural noun is temperatures.
The word aisle is a singular noun. The plural noun is aisles.
The noun teeth is plural.The plural form is tooth.
The noun 'orchid' is a singular noun, a word for one.The plural noun is 'orchids'.
The word moon is a singular noun. The plural noun is moons.