I really dislike the word "spiritual." It is one of those squishy, fuzzy words that everyone means something different by, and yet everyone continues to use it as if they mean the same thing. The only thing that everyone seems to agree on is that it is a good thing to be spiritual. This leads to bizarre arguments where people argue over who is spiritual, and yet it is clear to anyone who is not enamored with the word that what they are actually arguing about is the definition of the word itself.
Off the top of my head, I can think of the word being used to mean all of the following at different times:
1. Adherence to a particular religion (I recall, as a child, seeing some televangelist or another talk about how all non-Christians live "in spiritual poverty", for example).
2. Adherence to no particular religion, but a belief in some sort of divine force (which can range from a fuzzy feel-good sort of notion to a fairly clear and definite belief in a particular divine force, entity, or entities).
3. Abandonment of religions, but embracing of the idea of a largely undefined and mysterious divine force.
4. A sense of wonder about the universe (this definition is often used by atheists who wish to be considered spiritual).
5. Embracing of mysticism, which, depending on the individual, can range anywhere from a deep commitment to a mystical ideal to a superficial adoption of the trappings of mysticism.
...and, really, the list could go on for some time. While I wrote those, I came up with another ten possible definitions I have heard, plus each of those definitions can be further divided into more (deep commitment vs. superficial adoptions, formalized ritual vs. "free-form" exercise, etc.).
The point is, there are many different ways that the word is used, and many of these usages directly conflict with other usages. As a result, when someone is using it, unless you have them explain what they mean in detail, you'll really have little clue as to what they are saying. So, I consider the word to be useless. Actually, I consider it to be typically misleading, which is worse than useless.
This is different from a word such as "theory" which may be mis-used in many different ways, but comes from a particular place (in this case, science) where it has a specific meaning, and therefore can be guided back to the word's actual meaning. "Spiritual" has been a part of the general vocabulary for centuries, is not a specialized technical term, and as such can not be guided back to its "true" meaning, if it ever really had one to begin with.
To make matters more annoying, everyone insists on applying their definition of the term to everyone else. So, for example, I have always thought of the term as implying some sort of connection to the divine (as this is a common feature of all definitions that I have come across, save #4 above). So, when someone asks me if I am spiritual, I say "no." I don't believe that there is a divine force, and therefore I don't feel any connection to it.
However, this usually results in someone turning around and saying "yes you are! you're curious and always asking questions, that means that you're spiritual because you are seeking knowledge!"
Well, if the person has defined "spiritual" to mean "curious", then why not just use "curious" and do away with the ambiguity? Likewise, it is bizarre to watch those who hold to beliefs in the divine, spirits, etc. accuse members of more orthodox religions of being non-spiritual because they hold to traditions and old rituals, and to watch the members of orthodox religions accuse those who hold to the unorthodox beliefs of being non-spiritual because they don't hold to traditions and old rituals.
It seems to me that if we are going to insist on having a public dialogue about the "spiritual", we need to develop a vocabulary that is something other than a verbal Rorschach test. I suspect that the first step towards this is simply acknowledging that we all mean something different by this.
But I doubt that this will ever happen. The reality is that most folks don't even realize that they are arguing over definitions, and those who do seem to be more concerned with continuing the use of the term for their own purposes (because it has acquired positive social baggage despite the fact that it is a worse than useless term), than with actually communicating what they mean.