Plural: costumes
Singular: costume
Yes, the word 'costumes' is both a noun and a verb.The noun 'costumes' is the plural form of the singular noun 'costume'; a word for a type of clothing; a word for a thing.The verb 'costumes' is the third person, singular present of the verb to costume; meaning to provide or outfit with a costume.
The singular form of the demonstrative pronoun 'these' is this.
The singular form of "that" is "it."
it is already in its singular form.
The singular form is cuff.
"Stratum" is the singular form of stratum. The plural form is "strata".
The form hypothesis is the singular form. The plural form is hypotheses.
A singular form of dice is a die
The singular form of feet is foot.
The singular form of Oases is, Oasis.
The singular form of chromosomes is a chromatid.
"Wash" is the singular form of "wash."