Third-person singular simple present indicative form of stack.(verb)
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Use "stacks" in a sentence
"I get annoyed with email signatures laid out in stacks of vertical text 10 lines high."
"It's amazing how many liquor stores have no clue about the damage to their potential profit that buying on a wholesaler's "deal" can actually do to them -- especially when they invest in stacks of cheap spirits and plonk wine."
"Because the hypocrisy is just lying there -- in stacks of paper three feet high -- waiting to be exploited."