Just a little object lesson today in how a word's meaning can branch with time, like the delta of a river.
Once upon a time there was a Latin word incendere, which to burn. Its meaning is pretty much perfectly preserved in the word incendiary, especially incendiary weapons, which still set fire to things.
However, the word is also preserved in that to which fire is set, namely the incense that is burnt in the higher kind of church in a thurible.
And finally the word is preserved figuratively as a synonym for angry - incensed. This of course merely means that your passions have been fired, your tinderbox sparked and that you're about to explode like an incendiary in a censer.