plan vs outline

plan and outline both are nouns.

Word	Noun	Adjective	Verb	Adverb
plan	Yes	No	Yes	No
outline	Yes	No	Yes	No

As nouns, outline is a hyponym of plan; that is, outline is a word with a more specific, narrower meaning than plan:

plan (noun)	outline (noun)
scale drawing of a structure	a schematic or preliminary plan
a series of steps to be carried out or goals to be accomplished	a sketchy summary of the main points of an argument or theory
an arrangement scheme	the line that appears to bound an object

plan (verb)	outline (verb)
make plans for something	describe roughly or briefly or give the main points or summary of
have the will and intention to carry out some action	trace the shape of
make or work out a plan for; devise	draw up an outline or sketch for something