In my view spirit is a symbolic word that comes from Latin spiritus which means breath (of god), breeze or air, a symbol of life. I believe both this and the Germanic word ghost are translations of the new testament Greek pneuma and the old testament Hebrew ruwach.
If you try to look at the nature of air through the eyes of people of that period I would suggest it would have these qualities - it is invisible but you can see its effect when it animates something, it is intangible but you can feel it when it moves towards you or you move towards it, if you try to grasp it you lose it, its source is unknown and yet it seems to be ever present, if you don't get it into you (inspiration), you die (expire). It's a short step from here to see that, perhaps, the Hebrew word neshama (translated as human soul) can mean breath, breathing, divine inspiration i.e. the breath of god in man, life. Of course, then it's easy to imagine evil spirits as breezes that blow one off course.
'Spirituality' could then be seen as an inner quest to discover the essence of life and remain ever conscious (of it). To do so, often entails inner stillness, sometimes called a centre of balance. Mental activity and emotions tend to be disturbances which distract from the task. To tie it to this topic, to remain ever conscious of the essence of life, is life eternal.