Alternative form of security by design

(Australia, New Zealand, South Africa, colloquial) Hi, hello. / (Canada, US, air traffic control, informal) Denotes the end of a radio transmission.

(rare) castle-like: built or shaped like a castle. / (rare) Castled: having or furnished with castles. / (rare) Housed or kept in a castle.

An action or situation that is not a choice.