British spelling vs synthesise

British spelling is a noun but synthesise is not a noun.

Word	Noun	Adjective	Verb	Adverb
British spelling	Yes	No	No	No
synthesise	No	No	Yes	No

British spelling (noun)	synthesise (noun)
English orthography used in the UK, Ireland and most of the Commonwealth (characterized by 'analyse', 'centre' and 'useable')

British spelling (verb)	synthesise (verb)
	combine so as to form a more complex, product