Relating to, characterized by, or of the nature of convulsions; involving sudden violent movements.
From convulsion (from Latin convulsio, the noun form of convellere) plus the suffix -al (from Latin -alis), meaning 'relating to' or 'of the nature of.'
Words ending in -ional often describe abstract relationships to concepts—like 'national' relates to nation and 'convulsional' relates to the whole phenomenon of convulsing!
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