I think words can, and do, change from their original meanings. In fact, according to the Merriam-Webster Dictionary online, the word “spirit” was derived from the Latin words for “breath” and “to breath.” Since a person’s spirit was considered to be his or her life, and an easy way to tell if someone is alive is by whether or not they are breathing, it makes perfect sense. The definition of “spirit” as in “the ghost in the machine” was forged in a time when it was assumed that the difference between living and non-living things was that living things contain some sort of supernatural “life force” (see “vitalism“) and non-living things did not.
Now we are reasonably sure that this is not the case, and that life is a perfectly natural and material phenomena. (And the line between living and non-living has actually turned out to be rather blurred and not so easily defined.) So since there is no such thing as the “vital force” that animates living things, does this mean we should therefore throw the concept of “spirituality” out the window? I don’t think so, because even though knowledge and reason tell us that we don’t have “spirit” in any sort of supernatural sense, we still experience the world as if we did. Besides, when people talk of spirit are they not usually talking of the emotional and mental side of the human experience? The private world inside our own heads, which sure doesn’t feel like it is coming from our material brain? These are things we know are real, and have only assumed were supernatual in the past when words like “spirit” and “spirituality” were coined.
Anyway, my point is that (unlike a lot of atheists I know) I think the concept of “spirituality” is a good one and worth holding onto. The word is not perfect, but I think for now it is the best one we have for its purpose.
There is a nice commentary about the word on DeConversion.com, and I have linked to it below.