adverb, adjective: Having one's identity concealed.
noun: 1. One whose identity is concealed. 2. The state of having one's identity concealed.
>From Italian incognito (unknown), from Latin incognitus (unknown), from in- (not) + cognitus, past participle of cognoscere (to get to know). Earliest documented use: 1638.
"Ancient tales of monarchs passing incognito among their subjects."
Of Magic and Daylight; The Economist (London, UK); Jan 13, 2011.