Word

Words were the basis of Carrionite science. Part of language, the choosing of one's words was an essential part of what made one a great poet or playwright, and thus the Tenth Doctor held that William Shakespeare's ability to always find the right words was part of what made him such a "genius". (TV: The Shakespeare Code)

The first Dalek whom open fired upon Davros claimed to have no understanding of the word pity, it not being registered in his vocabulary bank. (TV: Genesis of the Daleks)

Other references
Conversations could be refered to as "a word", especially when one requested to speak with another.. (TV: Boom Town, Love & Monsters)