From WordNet (r) 3.0 (2006) :
stacks n 1: a large number or amount; "made lots of new friends"; "she amassed stacks of newspapers" [syn: tons, dozens, heaps, lots, piles, scores, stacks, loads, rafts, slews, wads, oodles, gobs, scads, lashings] 2: storage space in a library consisting of an extensive arrangement of bookshelves where most of the books are stored