Firewall

[fahyuh r-wawl] /ˈfaɪərˌwɔl/

noun
1.
a partition made of fireproof material to prevent the spread of a fire from one part of a building or ship to another or to isolate an engine compartment, as on a plane, automobile, etc.
2.
a person, thing, or event that acts as a barrier or protection against something undesirable:
The new employee handbook should create a firewall against unethical business conduct.
3.
Digital Technology. an integrated collection of security measures designed to prevent unauthorized electronic access to a networked computer system.
noun
1.
a fireproof wall or partition used to impede the progress of a fire, as from one room or compartment to another
2.
(computing) a computer system that isolates another computer from the internet in order to prevent unauthorized access
n.

1851 as a physical wall meant to prevent the spread of fire in a structure, from fire (n.) + wall (n.). Computer sense is by 1990.
firewall
(fîr’wôl’)
A software program designed to protect a network by preventing unauthorized users from gaining access or by monitoring transfers of information to and from the network.

A means of separating a computer network from outside networks for security purposes. A server outside an organization’s own network may be used to funnel all incoming and outgoing traffic to assist in keeping out viruses, as well as to prevent unauthorized outsiders from gaining access to a network.

noun

[fr a firewall built to contain a fire in a building, a meaning found by 1851, and a barricade between an engine and a passenger compartment, found by 1947]

1. firewall code.
2. firewall machine.