Is there a Korean→English dictionary installed on Ubuntu?
If there are several ones, which one could be considered the most complete?
Something like Gjiten for Japanese→English would be good.
Are u looking for a offline or online dictionary. If you are looking for an offline dictionary then you have to install it manually. The one which comes with Ubuntu is online dictonary. I think it can be customized for your requirement.
After extensive search I found GoldenDict is the best offline dictionary application available for Ubuntu. It is just the application . You have to install the dictionary database, which you can get it for free from GoldenDict site. It supports many dictionary formats, you will not have trouble finding the dictionary. Just check out the site, I hope you will get the dictionary database for Korean->English.
To install goldendict in Ubuntu run: sudo apt-get install goldendict