The plural of papyrus is papyri or papyruses. Both are acceptable, but papyri is preferred.
Because it is derived from the Greek -us form, the word "papyrus" (reed paper, or a document written on it) has the plural form "papyri".
There is no plural form for the word, countries. This word itself is a plural.
papyri
The plural of diary is diaries.
The plural form of the word 'deed' is 'deeds'.
The plural form of the word gelato is gelati.
The noun papyrus can be countable or uncountable. In more general, commonly used, contexts, the plural form will also be papyrus. However, in more specific contexts, the plural form can also be papyri e.g. in reference to various types of papyri or a collection of papyri
The plural form for the demonstrative pronoun this is these.
The plural form of the word "inferno" is "infernos."
The plural form of the word "ranch" is "ranches."
There is no plural form for the word, countries. This word itself is a plural.
There is no plural word for if.
The plural form is data.
papyri
The plural form for the word 'pioneer' is pioneers.
The plural form of the word "baby" is "babies."
The plural form of the word "pharynx" is "pharynges."
The plural form of vow is vows.