The Ish are possibly one of the strangest species ever encountered by humanity. They are a sapient memetic lifeform which manifests itself as the suffix "ish", whether spoken, written or simply thought. The Ish is described as a "metavore", as it feeds on the meanings of linguistic terms, absorbing word after word within the minds it inhabits and rendering the subjects in a zombie-like state, unable to communicate anything other than "Ish".
The Ish originated as an affix of the Omniverbum: an infinitely long word. As a linguistic singularity, the Omniverbum is to meaning as a black hole is to matter. It originated in the first instants after the Big Bang, when the universe was still small and condensed enough that sound could travel through it. The inhabitants of the planet Xenocubis, where the Ish was first found, believe that all of creation originated as that primordial word, and everything else since represents corrupted or distorted echoes of that word.
According to the Doctor, there are many other linguistic life forms besides the Ish, most of which aren't as hostile. This may imply that there is as much diversity among memetic species as there is among physical ones.
- Doctor Who audio story - ...Ish (2002)