large indefinite amount vs large indefinite quantity

large indefinite amount and large indefinite quantity both are nouns.

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

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

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

large indefinite amount (noun)	large indefinite quantity (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