One who or that which arises; something or someone characterized by rising up or emerging.
From arise (to get up, to emerge) combined with the agent noun suffix -er, which creates nouns meaning 'one who does' or 'one that is characterized by' a quality.
Ariser is a beautiful example of English's productivity—you can add -er to almost any verb to create an agent, so even uncommon combinations like 'ariser' work perfectly and are instantly understood by any English speaker.
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