Unknown and Unheard of

Unknown adjective - Happening or existing without one's knowledge.

Unheard of and unknown are semantically related in obscure topic. In some cases you can use "Unheard of" instead an adjective "Unknown", when it comes to topics like unfamiliar.

Nearby Words: unknowable, unknowing

Unknown and unheard of are semantically related in unique topic. You can use "Unknown" instead an adjective phrase "Unheard of", if it concerns topics such as out-of-the-way, unfound.