When describing a large amount or quantity of something, there are various synonyms that can be used instead of "large indefinite quantity". Some of these include: copious, ample, abundant, plentiful, excessive, lavish, substantial, significant, profuse, and vast. Each of these words adds a slightly different connotation to the amount being described, such as copious suggesting a plentiful amount that may even be overwhelming, or lavish implying an excessive or extravagant quantity. Using different synonyms can add variety to one's writing and make it more interesting and engaging.