lock down

Short definition from Wiktionary

Verb

1. 1
   To secure (something).
2. 2
   To secure (something): To blockade and lock (e.g. a building or campus) so as to prevent ingress or egress; to make the occupants (of an area) stay locked indoors for their safety.
3. 3
   To secure (something): To limit the use of (a computer network) to only users with permission.
4. 4
   To make (an arrangement) secure, definite, or permanent; to fix.
5. 5
   To cause (another person) to enter into an exclusive romantic relationship.
6. 6
   To travel through a flight of locks on a waterway in a downhill direction.

Noun

1. 1
   Alternative form of lockdown.