> I think of "polyfill" as filling many different holes to make it so you can forget about the different cases (browser compatabilities in this case). A polyfill pours concrete over a bumpy surface and makes its smooth.

Kind of like a façade then[1]? A shim would probably be synonymous with an (very informal) adapter.

[1] http://en.wikipedia.org/wiki/Facade_pattern

[2] http://en.wikipedia.org/wiki/Adapter_pattern