British spelling: causing disillusionment; revealing uncomfortable truths (present participle form).
Present participle of 'disillusionise' + -ing. The British '-ising' ending derives from Old French '-isant,' creating an ongoing or habitual adjective form.
British English maintains parallel '-ising' and '-izing' for different regions, but this particular word is so rare that you're unlikely to encounter 'disillusionising' even in Oxford or Cambridge publications—most writers just use 'disillusioning.'
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