Unsung and Unheard of

Unsung adjective - Not widely known.

Unheard of and unsung are semantically related In some cases you can use "Unheard of" instead an adjective "Unsung".

Unsung and unheard of are semantically related in unknown topic. Sometimes you can use "Unsung" instead an adjective phrase "Unheard of", if it concerns topics such as obscure, unique, out-of-the-way.