means At a future time, after the present moment but usually left vague about exactly when.

from From Old English æter, the comparative of læt, "late" — literally "more late." The same Germanic root surfaces in the German lass and is a distant cousin of the Latin lassus, "weary." So when you say "later," you are quietly pledging to do something at an ever-more-late hour, which is, perhaps fittingly, the most honest part of the promise.