The singualr form of critics is critic.
The singular form of the demonstrative pronoun 'these' is this.
The singular form of "that" is "it."
The singular form of "cuffs" is cuff.
The singular form of "stratum" is "stratum." The word does not change in its singular form.
Critics is a noun. It's the plural form of critic.
The singular form of feet is foot.
The singular form of scissors is "scissor."
The singular form of diagnoses is diagnosis.
The singular form of "wash" is "washing."
The singular form of "dice" is "die."
The singular form of "oases" is "oasis."
The singular form of vixen is "vixen." Both the singular and plural form of this word are the same.