Google adsense officially announced adsense for domains. If you own a domain which is not used you can park with Google Adsense.

If you get some traffic for your domain, then you can get some earnings with the unused domain. Log in to your Adsense account and move to Adsense setup you can find Adsense for domains. Read the TOS of Google Adsense for domain and apply for it.

Point your domain A record and CNAME record to Google server as shown below.

Detailed information about domain setup. After completing domain setup as said above wait for few hours adsense team will verify your domain and settings. Finally you can earn with your domain.