This is one of those words that I'm reluctant to list because it's such an obvious alteration of well-known words. On the other hand, it's one of the few words I've listed that's actually relatively new, instead of just new to me.
So: "satnav" means "satellite navigation system."
I encountered it in an article in April titled "UK's Queen celebrates 80th birthday," which contains the following sentence:
From the age of the steam train to the era of satnav, she has been on the throne through it all.