systematic desensitisation vs British spelling

systematic desensitisation and British spelling both are nouns.

Word	Noun	Adjective	Verb	Adverb
systematic desensitisation	Yes	No	No	No
British spelling	Yes	No	No	No

systematic desensitisation (noun)	British spelling (noun)
a technique used in behavior therapy to treat phobias and other behavior problems involving anxiety; client is exposed to the threatening situation under relaxed conditions until the anxiety reaction is extinguished	English orthography used in the UK, Ireland and most of the Commonwealth (characterized by 'analyse', 'centre' and 'useable')