THE WORD spirit has come to mean something pale and shapeless, like an unmade bed. School spirit, the American spirit, the Christmas spirit, the spirit of '76, the Holy Spirit—each of these points to something that you know is supposed to get you to your feet cheering, but that you somehow can't rise to. The adjective spiritual has become downright offensive. If somebody recommends a person as spiritual you tend to avoid that person, and usually with good reason. Inspiring is even worse. Inspirational is worse still. Inspirational books are almost invariably for the birds.
Like its counterparts in Hebrew and Greek, the Latin word spiritus originally meant "breath" (as in expire, respiratory, and so on), and breath is what you have when you're alive and don't have when you're dead. Thus spirit = breath = life, the aliveness and power of your life, and to speak of your spirit (or soul) is to speak of the power of life that is in you. When your spirit is unusually strong, the life in you unusually alive, you can breathe it out into other lives, become literally in-spiring.
Spirit is highly contagious. When people are very excited, very happy, or very sad, you can catch it from them as easily as measles or a yawn. You can catch it from what they say or from what they do or just from what happens to the air of a room when they enter it without saying or doing anything. Groups also have a spirit, as anybody can testify who has ever been caught up in the spirit of a football game, a political rally, or a lynch mob. Spirit can be good or bad, healing or destructive. Spirit can be transmitted across great distances of time and space. For better or worse, you can catch the spirit of people long dead (Saint Therese of Lisieux or the Marquis de Sade), of people whose faces you have never seen and whose languages you cannot speak.
God also has a spirit—is Spirit, says the apostle John (4:24). Thus God is the power of the power of life itself, has breathed and continues to breathe life into his creation. In-spires it. The spirit of God, Holy Spirit, Holy Ghost, is highly contagious. When Peter and his friends were caught up in it at Jerusalem on Pentecost, everybody thought they were drunk even though the sun wasn't yet over the yardarm (Acts 2). They were.