Incog

1846, Lydia Huntley Sigourney, "Forgotten Flowers", Voice of Flowers, page 64. Though we travel'd incog. yet we trembled with fear, For the accents of strangers fell hoarse on our ear.

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But his general aspect and manner were so suggestive of an education and career incongruous with his naval function that when not actively engaged in it he looked like a man of high quality, social and moral, who for reasons of his own was keeping incog.

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What—my old Guardian—what[!] turn inquisitor and take evidence incog.—

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Then you, ye auld, snick-drawing dog! Ye cam to Paradise incog, An’ play’d on man a cursed brogue, (Black be your fa’!)

Source: wiktionary