Qadosh

The Hebrew word most often translated as "holy" originally meant, and still has a secondary meaning of, "set apart." Sacredness is simply separation from the common.  "[C]ontact and contamination are at the heart of impurity"

(Also, Hebrew has a really interesting structure!)

Edit: (10/19/09) turns out lots of words meaning or related to "holy" have really interesting etymologies: the OED (not that one) has a relevant list.   The pre-Christian meaning of Old English "holy"

was probably "that must be preserved whole or intact, that cannot be transgressed or violated," and connected with O.E. hal (see health) and O.H.G. heil "health, happiness, good luck."

"That which must be preserved whole" is a fairly different root meaning than "that which is set apart."  They are almost opposite, in fact - wholeness against that which is divided.  And then again the Latin "sacred" (maybe) comes

from O.L. saceres, which Tucker connects to base *saq- "bind, restrict, enclose, protect," explaining that "words for both 'oath' & 'curse' are regularly words of 'binding.'

Which again is different.

That which is set apart, that which is whole, that which is bound.  I guess the meaning to complete the set would be something like, that which is freed.  And though I can't put a single word to it, I know that Buddhism's goal is nirvana, being set free of the wheel of existence.  "Nirvana" is actually a negative word in the Sanscrit,  I understand, meaning something like, "no wind blows." So that's clearly not quite it.  But something like it?