Searching with a "not" in Spotlight!
One thing that is weird about Spotlight is that it only seems to accept positive searches. You cannot say "contains" this and "doesn't contain" this.
The only option for "Contents" is "contains":
The same thing happens with "Name", there is "contains" and "is", but there is no "doesn't contain" and "is not":
The way around this that I found is to choose "contains" and to add a "-" in front of the word. So if you search for "Contents" "contains" "application -ical", it will search every file and document to find where it is written application, but it is not written ical. Make sure that there is no space between the "-" and the word or it won't work. That is the only way I found, but I think it is still an issue because the option of excluding files or names is not obvious and the "-" is not explained in the Finder help file.