There are times when only the word ‘passion’ will do. It’s a shame it’s so overused its real meaning has trickled away. ‘Passion project’ is horrible too.
Passion means being in a state of strong and barely controllable emotion. So if you’re passionate about, let’s say, sandwiches or rope, you need to get a life.
But when something triggers strong and barely controllable emotion in you, it can only be called passion.
Passion makes our world ours. Passion projects are resistance. If we’re lucky enough to be able to pursue them. But that’s another story.