[count] 1 a : an official mark that is stamped on paper or on a small piece of wax to show that something (such as a document) is genuine and has been officially approved ▪ The paperwork must have a notary's seal. b : a small piece of stamped wax or a small sticker that is put on a letter or envelope to keep it closed or to show that it has not been opened
2 : a device with a raised design that can be pressed into something (such as paper or wax) to make a seal
3 a : a piece of material (such as rubber) that is used on the lid of a container to keep air, water, etc., out of the container or to show the container has not been opened ▪ a rubber seal on the jar ▪ The plastic seal on the bottle was broken. b : the state of being closed tightly so that no air, water, etc., can pass through ▪ The caulk gives the window an airtight seal.