By Mary Morel
Insidious means treacherous or crafty.
He took power insidiously.
It was an insidious plot.
Invidious means likely to give offence.
He made invidious remarks.
It was an invidious comparison.
One letter separates these two words, but they come from different Latin words.
Insidious derives from the Latin word for ambush, and invidious from a word meaning envy.