There is frustration in finding an English dictionary by searching the apt DB because there are lots of simple world lists and translation libraries which do not provide word definitions. This is worsened by the fact that Artha is not even described as a dictionary. IIUC, a dictionary is in fact the primary purpose of Artha. I have no idea why the author just describes it as a thesaurus, but in this case the Debian package should probably not just be a copy of the upstream description. This was reported upstream 12 years ago: https://bugs.launchpad.net/artha/+bug/998635