large indefinite quantity vs large indefinite amount

large indefinite quantity and large indefinite amount both are nouns.

Word	Noun	Adjective	Verb	Adverb
large indefinite quantity	Yes	No	No	No
large indefinite amount	Yes	No	No	No

As nouns, large indefinite quantity and large indefinite amount are synonyms defined as:

large indefinite quantity and large indefinite amount: an indefinite quantity that is above the average in size or magnitude

large indefinite quantity (noun)	large indefinite amount (noun)
an indefinite quantity that is above the average in size or magnitude	an indefinite quantity that is above the average in size or magnitude