Done in a sneaky or stealthy way, taken without permission or notice.
From Latin arreptus, past participle of arripere 'to seize,' combined with -titious (as in surreptitious). The prefix ar- means 'to' and rapere means 'to seize,' so the word literally means 'seized to' or taken away.
This is basically the shy cousin of 'surreptitious'—while surreptitious (literally 'under-seized') became the common word for sneaky actions, arreptitious preserves an older Latin root that emphasizes the act of seizing rather than hiding.
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