synthesize vs synthesise

synthesize and synthesise both are verbs.

Word	Noun	Adjective	Verb	Adverb
synthesize	No	No	Yes	No
synthesise	No	No	Yes	No

As verbs, synthesize and synthesise are synonyms defined as:

synthesize and synthesise: combine so as to form a more complex, product

synthesize (verb)	synthesise (verb)
combine so as to form a more complex, product	combine so as to form a more complex, product
combine and form a synthesis