Slang

The Valeyard identified the adjective "barmy" as a "rather imprecise" Earth slang word which implied psychiatric instability. (TV: Mindwarp)
 
Jack Harkness identified the adjective "cheesy" as early 21st century slang. When asked, Mickey Smith clarified that it was bad, though Jack believed that bad meant good. (TV: Boom Town) Yasmin Khan would describe Jack as "good cheesy". (TV: Fugitive of the Judoon)
When Luke Smith used "bugging around" instead of "mucking" or "messing around", Clyde Langer advised him that words were important in slang and that he could not improvise. (TV: Warriors of Kudlak)
Wilfred Mott asked Donna Noble if "little blue box" was slang for something when she asked if he had seen one. (TV: Partners in Crime)
Cockney rhyming slang was when one word was replaced by another word or phrase that rhymed. Leela noted that it was like a code, when she first learnt about it. (AUDIO: Dead Men's Tales)