A partisan may be
either a person who is a strong supporter of a (political) party, faction, or cause, and disposed to puts its interests and aims before other interests and aims which should take precedence,
or a member of an armed resistance group formed to oppose a government or army of occupation – e.g., a member of the Free French forces which fought against the German army of occupation in France during the Second World War.
The word ‘partisan’ is also used as an adjective, meaning ‘of, related to, or characteristic of a partisan (in either of the above senses)’ – as in ‘The debate in the House of Commons was conducted in a partisan spirit: most speakers failed to consider the issue from the point of view of the national interest’ and ‘The activities of the various partisan forces in France during the Second World War contributed to the eventual defeat of the German army of occupation.’
This word partisan, whether used as a noun or an adjective, may be pronounced with the stress on the first or the final syllable, but in either case with the final syllable clearly articulated and rhyming with ‘fan’ or ‘ran’ IPA: /'pɑː tɪ ,zæn or ,pɑː tɪ 'zæn/. There is another word ‘partisan’, spelt identically but pronounced differently – i.e., the two words are homographs but not homophones. This second word is pronounced with the stress on the first syllable, but with the final syllable a mere Schwa, i.e., a short, unstressed ‘er’ sound, IPA: /'pɑː tɪ ,zən/. A partisan in this sense was a type of spear used by soldiers in Europe during the Middle Ages: it had, on either side of the spearhead, two opposed axe blades or spikes, which helped the user to parry sword thrusts.
Both words may be spelt with a 'z' in place of the 's', i.e., partizan.