line of defence vs Australian spelling

line of defence and Australian spelling both are nouns.

Word	Noun	Adjective	Verb	Adverb
line of defence	Yes	No	No	No
Australian spelling	Yes	No	No	No

line of defence (noun)	Australian spelling (noun)
defensive structure consisting of a barrier that can be employed for defense against attack	English orthography used in Australia (characterized by 'analyse', 'centre', 'usable')
any organization whose responsibility it is to defend against something