Elisp: Search a File Without Visiting?

[taashlo]

I've looked throught the elisp manual without finding the answer to
my question.  I've written some elisp so that when I hit a key
sequence (C-ct) a thesaurus lookup of the word at point (or the
phrase with the mark) is performed with the results of the search
displayed in a separate window (for further searching or dictionary
lookup).

This currently works, but it relies on loading the entire thesaurus
file into a buffer to search for the word.  The problem is that the
thesaurus file (mthesaur.txt[1]) is about 24MiB.

My question: is it possible (using elisp) to search the contents of
the thesaurus file *without* loading it into a buffer?

Thanks,
Tad

[1] ftp://ibiblio.org/pub/docs/books/gutenberg/etext02/mthes10.zip