Real - Realistic, Authentic, Certain, Legitimate, Solid, Existent, Substantive, Evident.
Busy - Active, Unavailable, Occupied.
Believe - Admit, Consider, Conceive, Regard, Understand, Conclude, Affirm, Suppose.
Poisonous - Deadly, Toxic, Lethal, Fatal, Virulent, Noxious, Vicious.