General synonyms:
* Departing
* Exiting
* Going
* Quitting
* Retiring
* Stepping down
* Taking off
* Moving on
* Going away
More specific synonyms:
* For a place: Departing, exiting, moving out, vacating, abandoning
* For a job: Resigning, quitting, retiring, stepping down, terminating
* For a relationship: Breaking up, separating, ending, parting ways
* For a task or activity: Abandoning, stopping, discontinuing, ceasing
More formal synonyms:
* Departing
* Exiting
* Retiring
* Ceasing
The best synonym for "leaving" depends on the specific context of the sentence.