luncheon meeting vs lunch meeting

luncheon meeting and lunch meeting both are nouns.

Word	Noun	Adjective	Verb	Adverb
luncheon meeting	Yes	No	No	No
lunch meeting	Yes	No	No	No

As nouns, luncheon meeting and lunch meeting are synonyms defined as:

luncheon meeting and lunch meeting: a meeting for lunch; usually to conduct business while eating

luncheon meeting (noun)	lunch meeting (noun)
a meeting for lunch; usually to conduct business while eating	a meeting for lunch; usually to conduct business while eating