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To close something and bind the seals so it does not reopen. A noun or pronoun can be used between "seal" and "up." They're going to seal up the door leading into the cellar. Would you please seal this box up for me so I can get it in the mail?
1. Sealed shut (by some means). That old house has been sealed up for nearly 15 years. The box was sealed up with three different locks.
2. Completely finalized or definitively resolved. We're hoping to have this deal sealed up by the end of the week. The whole thing's sealed up—there's nothing more I can do.
mod. settled; secured; cinched. The matter was sealed by Monday morning.