obscure (UNCLEAR)
adjective 
unclear and difficult to understand or see 
Official policy has changed, for reasons that remain obscure.
They talk in an obscure jargon that's almost impossible to understand.

obscure
verb [T] 
Two new skyscrapers had sprung up, obscuring (=hiding) the view from her window. [T]
The sun was obscured (=hidden) by clouds. [T]
Managers deliberately obscured the real situation from federal investigators (=made it difficult for them to discover and understand it). [T]

obscurity
noun [U] 
The obscurity of the language means that few people are able to understand the new legislation.