Webster's Revised Unabridged Dictionary · 1913

Incognito

Incognito , a. o adv.

[Italian incognito, masc., incognita, fem., Latin incognitus unknown; pref. in- not + cognitus known, past participle of cognoscere: compare French incognito, from It. See Cognition.]

Without being known; in disguise; in an assumed character, or under an assumed title; -- said esp. of great personages who sometimes adopt a disguise or an assumed character in order to avoid notice.
'T was long ago Since gods come down incognito. — Prior
The prince royal of Persia came thither incognito. — Tatler

Incognito (#) , noun

[See Incognito, a.]

1.
One unknown or in disguise, or under an assumed character or name.
2.
The assumption of disguise or of a feigned character; the state of being in disguise or not recognized.
His incognito was endangered. — Sir W. Scott