It means a word that refers to multiple things.
For example, the word "tree" refers to one tree, but its plural form "trees" refers to 2 or more trees.
you ( plural or polite form)
There is no such word. If you mean thankful, there is no plural.
The word marriage is not a plural form; the plural form for the noun is marriages. Or, perhaps you mean monogamy, the opposite of polygamy.
It is the plural form of the possessive pronouns: His, her, their.
The singular noun is mean, the plural form is means.
rose plural form
The word 'utilidades' is a Spanish noun in the feminine plural form. Although its singular form is translated directly as 'utility' or 'usefulness', in its plural form it is interpreted to mean 'profits'.
I hope you mean "stylo"; if you do, it's short for stylograph, the plural form of which is stylographs. I assume that the plural form for the shortened form would also be no more than an added S to the word.
the (plural) in masculin form
The word "if" is a usually a conjunction, which has no plural. However, it can be used as a noun to mean a possibility, with the plural form being ifs (e.g. no ifs, ands, or buts).
If you mean rhinoceros, the plural is rhinoceroses ( although a plural form rhinoceros may be encountered also).
Not sure what you mean by deligance, but the plural form of honesty is honesties.