..solo?
Duo? otherwise, duet...
The word 'duo' is the singular form; the plural form is duos.
Yes, duet is a noun, a singular common noun.
The plural form of duet is duets.
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.