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To affix something at an elevated level onto some surface by driving a nail or some similar fastener through both. A noun or pronoun can be used between "nail" and "up." I tried nailing the picture frame up on the wall, but it was too heavy for the flimsy drywall to hold. I'm going to nail up a sign out front so people know that our dog will bite them if they try to trespass on our property.
nail something up
1. to put something up, as on a wall, by nailing. Please nail this up. I'll nail up this picture for you.
2. to nail something closed; to use nails to secure something from intruders. Sam nailed the door up so no one could use it. Who nailed up the door? I can't get in!