Source: Oxford Dictionaries

Bird Chorus: He’s a nasty bird!
Nigel: I’m insidious.
Bird Chorus: He’s ghastly!
Nigel: Oh, I’m hideous!
Bird Chorus: He was a real macaw!
Nigel: I’m a cockatoo!
Bird Chorus: An obscene bird!
Nigel: Yes, that bit’s true.
– “Pretty Bird“, Rio (2011)

Okay, maybe I’ve had a couple of Jemaine Clement songs stuck in my head recently (thanks, Moana), so I felt like sharing a vocabulary word from one of them. The above excerpt is from the full version of “Pretty Bird” from the 2011 film Rio, a song Nigel sings to reveal his backstory to Blu and Jewel and establish his status as the villain. This example may not show today’s featured word in its primary sense, but it’s still easy to understand in context; Nigel is indeed an “insidious” cockatoo!

To be “insidious” is to proceed in a subtle and gradual way with harmful effects. The word arose in the mid 16th century and comes from the Latin adjective insidiosus, meaning “cunning”. This adjective stems from the noun insidiae “ambush”, which derives from the verb insidere “to lie in wait”. This verb comprises two roots: the preposition in “in” and the verb sedere “to sit”.

Aside from its main definition, “insidious” can also be used as a synonym for “treacherous” or “crafty”. This is arguably its most common use in modern speech, though its primary meaning can be just as useful in more formal contexts (such as an “insidious” disease). Either way, you can be sure this adjective always has a negative connotation. If you write characters with a crafty nature or actions that cause harm over time, you may find a place for the word “insidious” in your stories!

What are your thoughts on this word? Any suggestions for future “Word of the Week” featured words?