incognito

1. not comparableWithout being known; in an assumed character, or under an assumed title; in disguise.

   THE Scepticks think 'twas long ago, / Since Gods came down Incognito; / To ſee who were their Friends or Foes, / And how our Actions fell or roſe.

   1703, Mat[thew] Prior, “The Ladle”, in Poems on Several Occasions, London: […] Jacob Tonson […], published 1709, →OCLC, stanza 1, page 125

1. not comparableWithout revealing one's identity.

   The prince royal of Prussia came thither incognito.

   1709 May 29 (Gregorian calendar), Isaac Bickerstaff [et al., pseudonyms; Richard Steele et al.], “Wednesday, May 19, 1709”, in The Tatler, number 17; republished in [Richard Steele], editor, The Tatler, […], London stereotype edition, volume I, London: I. Walker and Co.; […], 1822, →OCLC

   1 more example

   "But you can understand," said our strange visitor, sitting down once more and passing his hand over his high white forehead, "you can understand that I am not accustomed to doing such business in my own person. Yet the matter was so delicate that I could not confide it to an agent without putting myself in his power. I have come incognito from Prague for the purpose of consulting you."

   1891 June 25, A[rthur] Conan Doyle, “Adventures of Sherlock Holmes. Adventure I.—A Scandal in Bohemia.”, in Geo[rge] Newnes, editor, The Strand Magazine: An Illustrated Monthly, volume II, London: George Newnes, Limited, […], published July 1891, →OCLC, page 65, column 2

plural incognitos

1. countableuncountableOne unknown or in disguise, or under an assumed character or name.
2. countableuncountableThe assumption of disguise or of a feigned character; the state of being in disguise or not recognized.

   Of those letters, and other attempts of the same kind, the author could not complain, though his incognito was endangered. He had challenged the public to a game at bo-peep, and if he was discovered in his “hiding-hole,” he must submit to the shame of detection.

   1829 January 1, Walter Scott, “General Preface”, in Waverley (Waverley Novels; I), Edinburgh: […] Cadell & Company; London: Simpkin and Marshall, page xxxii

   1 more example

   It contained a letter from the King himself, craving hospitality for a few days, as his mother was about to visit England, and to take up with Lord Avonleigh her residence at the Castle. A slight incognito would be preserved, and as little form and ceremony expected as was possible.

   1834, L[etitia] E[lizabeth] L[andon], chapter XX, in Francesca Carrara. […], volume III, London: Richard Bentley, […], (successor to Henry Colburn), →OCLC, page 169