stackstack2 verb1[transitiveT] to put things into neat pilesThe supermarkets failed to stack the shelves during opening hours.
2[intransitiveI, transitiveT] to put a group of people, or vehicles or other things in a particular order as they wait to do somethingThe two airliners were stacking as they waited to land.
—stacking noun [uncountableU]a machine that prepares huge bags of salt for stacking