If something is totally unavoidable, it is inevitably going to happen. Inevitably, the sun will come up tomorrow.
The adverb inevitably comes from the negative of the French word for "avoid" or "shun." There are things you can put off for a while, but inevitably you're going to have to deal with them at some point, like telling your family that you crashed the car. No matter how free-spirited you imagine yourself, unless you are independently wealthy, you will inevitably have to settle down and get some sort of job, like writing and editing word definitions.