action vs follow up

action is a noun but follow up is not a noun.

Word	Noun	Adjective	Verb	Adverb
action	Yes	No	Yes	No
follow up	No	No	Yes	No

action (noun)	follow up (noun)
the most important or interesting work or activity in a specific area or field
a judicial proceeding brought by one party against another; one party prosecutes another for a wrong done or for protection of a right or for prevention of a wrong
something done (usually as opposed to something said)
a military engagement
an act by a government body or supranational organization
the operating part that transmits power to a mechanism
In firearms terminology, the mechanism that handles the ammunition (loads, locks, fires, and extracts the cartridges).
the trait of being active and energetic and forceful
the series of events that form a plot
a process existing in or produced by nature (rather than by the intent of human beings)
the state of being active

action (verb)	follow up (verb)
put in effect	pursue to a conclusion or bring to a successful issue
institute legal proceedings against; file a suit against	increase the effectiveness or success of by further action