To make something definite; to establish something clearly as final or certain (British spelling variant).
From definite plus -ise/-ize (verb-forming suffix). The -ise suffix is British, while -ize is American. Both trace to Greek -izein.
British English uses -ise endings while American uses -ize, creating pairs like 'organise/organize' and 'finalise/finalize.' 'Definitise' is rarer but follows this pattern—turning an adjective into an action verb.
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