Out-of-bounds and Unobtainable

Out-of-bounds adjective - Outside the foul lines.

Unobtainable and out-of-bounds are semantically related. In some cases you can use "Unobtainable" instead an adjective phrase "Out-of-bounds".

Unobtainable adjective - Hard or impossible to get to or get at.

Out-of-bounds and unobtainable are semantically related. Sometimes you can replace phrase "Out-of-bounds" with "Unobtainable", this terms are similar.