Is nothing holy?
With Madonna on tour, "The Da Vinci Code" in theaters, and skinny jeans coming back into style, sacrilege has been on my mind.
The oft-misspelled adjective is sacrilegious, not sacreligious.
It's easy to see why a term referring to "gross irreverence toward something held sacred" is often thought to contain the word religious.
But popular belief assigns the words different origins: sacrilege from the Latin sacrum legere, "to steal sacred things" and religion from the Latin religionem, via religare, "to bind fast." (Some, including Cicero, have argued that religionem derived from relegare, "go through again, read again," from re- "again" + legere "read," but that theory has fallen out of favor. It would, however, give sacrilege and religion a shared origin. And let me stop here before I make a fool of myself; etymology is not my strong suit.)
In any case, I still get tripped up when writing sacrilegious; my brain wants to throw in some religion. But as soon as I think of sacrilege, I manage to keep the spellings straight. (Others aren't so lucky.)
If that doesn't work for you, try this mnemonic device: Remember that religious is e-i; sacrilegious goes against that, i-e.