How do you spell plural form of possess?

Answer 1

Possess is a verb. Its plural form (the one used with plural subjects) is possess, while the form used with singular subjects is possesses.

Examples:
We possess, they possess.
He, she or it possesses.

The noun form of possess is possession, plural possessions.

Answer 2

It is a verb, not a noun, so possess is already the plural form. Possesses is the singular verb form. The verb pluralization rules are opposite the noun pluralization rules that most know.

"He possesses." <-- Singular

"We possess." <-- Plural

Possession would be the noun form, and the plural of possession is possessions.

"This watch is my most prized possession." <-- Singular

"The fire took all of our possessions." <-- Plural