(uncountable) The state, property or quality of being hidden. / (countable) The result or product of being hidden.

plural of hiddenness

Located or positioned out of sight; not visually apparent. / Obscure.

past participle of hide

plural of hidden agenda

(taxation) A tax that is not visible to the consumer at the point of retail, having been levied on intermediate products, such as inputs to a finished product, or outputs from raw material production.

(physics) any parameter that would supplement quantum mechanics so as to make it like classical mechanics; local hidden variables have been proved to be inconsistent with quantum mechanics

A wish (and plan) to implement a particular idea without telling anybody, even though people may be affected in a negative way.

past participle of hide away

(aviation) A connecting city between the origin and destination of a passenger flight, where a passenger can save money on the airfare by disembarking at the connecting city rather than continuing to the destination.