"plan" is an adjective but when it is written with an "s" as in "plans" is it considered as a noun or no??
"Plan" is not an adjective.
Both "plan" and "plans" are used as nouns or verbs.
Examples:
I will plan the party. (verb)
He plans to study archaeology. (verb)
We are making plans for the next reunion. (noun)
Voters approved the plan for a new school building. (noun)