Today's word is another one we slipped out of Latin when
it wasn't looking.
What does it refers to in this case?
the whole paragraph:
Word History: Today's word is another one we slipped out of Latin when it wasn't looking. Latin
taciturnus comes from the noun tacitus "silent", the past participle of tacere "to be silent". A related word is tacit "unspoken but implied", which we also use freely. Few other words seem related to this stem. However, one famous name is Cornelius Tacitus (ca. 55-120) who, despite being named Silence, was one of the most elegant orators and historians of his day. (We are, of course, most grateful that Luis Alejandro Apiolaza is not taciturn when he thinks of very Good Words like this one, which he suggested for today.)
(
http://www.alphadictionary.com/goodword/word/taciturn)