'Jackhammer' is the singular form.
The singular form of the word "criteria" is "criterion."
The word 'duo' is the singular form; the plural form is duos.
The singular form of the word flagella is flagellum.
The singular form of the word "señores" is "señor."
That is the singular form; the plural form is those.
The singular form is commando.
The singular possessive form of the word "jury" is "jury's."
The word dog is the singular form.
"Biopsy" is the singular form, while "biopsies" is the plural form.
The singular form of Sioux is "Sioux." It is both the singular and plural form of the word.
The singular form of the word "possum" is possum. The plural is possums.
The word hypopharynx (one word) is the singular form; the plural forms are hypopharynges or hypopharynxes.