Polysemous

The word 'head' is polysemous because it can refer to both the organ and a leader. 

Friendship is viewed as the sine qua non in a relationship. 

In addition to the iodide, some of the fatty base had osmosed to the membrane in each case. 

He must have been incandescent when he was in government. 

I thought the idea was that you would make scintillating conversation.