I've seen and heard the word "tnetennba" used, most famously by Moss in Season 4, Episode 2 of the IT Crowd. Here's a short clip with it.
Essentially, Moss was a contestant on a fake episode of the TV show Countdown. In this episode, no definition of the word is given but, when asked, Moss uses the word in a sentence as follows;
Good morning, that’s a nice tnetennba
I am trying to establish whether this is a real word or not, which is difficult since language is always changing. I've found multiple sites stating that the word was made up purely for the show and some others saying that the word itself is nothing more than a mechanism for generating traffic to a website, among others.
Is "tnetennba" a real word, and if so, what does it mean?