v.1. To arrange something in a stack; pile something: I stacked up the magazines in orderly piles. Don't leave newspapers all over the floor; stack them up neatly.
2. To form into or as if into a stack; accumulate: I've been away for two weeks, and my mail is stacking up.
3. To equal or be of similar quality: The salary and benefits at this company don't stack up against those offered by larger companies.
4. To rank against one another; bear comparison: We sent our critic out to see how the local restaurants stack up.
5. To make sense; add up: The story he gave the police was full of contradictions—it just didn't stack up.
6. To direct or cause some aircraft to circle at different altitudes while waiting to land: The control tower stacked up the planes until the runway could be cleared. The controllers stacked the planes up because only one runway was open.