Insidious vs invidious

In the series 'words almost spelled the same and almost mean the same thing, but are not'

Insidious and invidious.

They both sound bad. One sounds like...well the other does, too. But they are distinct.

That snake slithering up towards you unannounced? Insidious. Shaking a snake in your face? Invidious. Both are pretty mean. Insidious is stealthy or under the radar. Invidious is plain ill will.

Insidious describes something that lies in wait to get you, and invidious is something offensive or defamatory. Cancer can be insidious, lurking in your body without your knowing it. Invidious doesn't hide; it's hateful right away.

Insidious didn't fall too far from the tree – it comes directly from the Latin word insidious meaning "deceitful, cunning, artful," from insidiae "plot, snare, ambush." That's pretty unannounced. Something insidious can even be attractive while doing harm, like an insidious plot to befriend your crush's girlfriend, so you can break them up. But often it's not attractive, just sneaky.

Invidious on the other hand is from the same place as envy. But it has slid over to mean just plain ill-will, where envy might come in but is not necessary.

You can be invidious in an insidious manner (being sneaky about your distaste for the other). But I think insidious carries enough negative feeling in there that it already includes the attributes of invidiousness.