Menisci is plural. Meniscus is singular.
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 binoculars is "binocular."
The singular form of "stratum" is "stratum." The word does not change in its singular form.
The form hypothesis is the singular form. The plural form is hypotheses.
The singular form of feet is foot.
The singular form of "dice" is "die."
The singular form of scissors is "scissor."
The singular form of diagnoses is diagnosis.
The singular form of "wash" is "washing."