How do you spell abscontion?

There is no actual noun for the verb abscond (to steal away), although absconsion has appeared in the past. It is used in some locales (e.g. South Africa) to mean abandonment of a job.

The gerund "absconding" is normally used when someone absconds, and the noun "abscondence" is used to mean hiding by a fugitive.

The similar anatomical term absconsio means a hollow or depression.