line of defence is a noun meaning "any organization whose responsibility it is to defend against something". It carries 2 recorded senses.
any organization whose responsibility it is to defend against something
“police are the major line of defense against crime”
defensive structure consisting of a barrier that can be employed for defense against attack
Definitions, synonyms and semantic relations for line of defence come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.