If you saw this on the site you knew I was going to use it soon. If not, never mind.

This phrase can be taken two different ways. It means AWOL, UA, or leaving with out announcing the fact.

In the 1600's in France, it was perfectly acceptable in French etiquette for a person to leave a party or gathering without informing the host and asking his permission or 'leave'. In other words you felt as though it was time to go and you left. And then by your own accord would return at the appointed time and place.

However, in British society this type of behavior was not at all acceptable. A person would ask if they may leave a party or gathering. In a similar vein a sailor would ask for time ashore.

So, we have two different countries and two different meanings for the same phrase.