What does on a wind and a prayer mean?

The phrase is actually "on a wing and a prayer" and it means to just about get the job done despite adversity and setbacks. The phrase originated in a rousing song from the second world war in which a war plane was described flying home badly damaged with one engine blown out, being held aloft by one wing and the prayers of its crew: on a wing and a prayer. One of our planes was missing

Two hours overdue

One of our planes was missing

With all its gallant crew

The radio sets were humming

We waited for a Word

Then a noise broke

Through the humming and this is what we heard

Comin' in on a wing and a prayer

Comin' in on a wing and a prayer

Though there's one motor gone

We can still carry on

Comin' in on a wing and a prayer

What a show, what a fight, boys

We really hit our target for tonight

How we sing as we limp through the air

Look below, there's our field over there

With just one motor gone

We can still carry on

Comin' in on a wing and a prayer