In a way that is striking, attention-grabbing, or stops people in their tracks.
From arrest (in the sense of 'to stop' or 'to catch attention') plus -ing (present participle) plus -ly (adverb marker). The meaning shifted from literally stopping to figuratively capturing attention.
This word evolved beautifully: while 'arrest' originally meant only to physically stop, by Shakespeare's time writers were using 'arresting' to mean something so striking it captures your attention like a physical force.
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