British spelling, present participle: the ongoing process of converting to or supporting abolitionist principles.
From abolitionise (abolition + -ise) plus the present participle suffix -ing, which generates continuous forms and verbal nouns in English.
When reading 19th-century British newspapers and political pamphlets, you'll see both 'abolitionising' (British) and 'abolitionizing' (American) used, and these spelling differences help historians pinpoint whether documents were published in London or Boston.
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