Rik Ellis, a British MMA fighter and son of AikiWeb poster Henry Ellis, posted on his blog: "For me, my Aikido is in my mind and my body." If you watch any of Rik's video clips you won't see Aikido expressed in the form that you are used to, yet he would probably tell you that he takes his Aikido into the cage with him, and uses it. Aikido isn't form, it's not techniques. The form and techniques are expressions of the Art of Aikido not the Art itself. What binds the many expressions of Aikido together are the principles.
From the Art of Peace: "The techniques of the Way of Peace change constantly, every encounter is unique, and the appropriate response should emerge naturally. Today's techniques will be different tomorrow.Do not get caught up with the form and appearance of a challenge. The Art of Peace has no form - it is the study of the spirit."
So if you would like to know,
why not simply let O Sensei provide it for you? Aikido "is the study of the spirit."
"The study of the spirit" is not a functional definition. If you tell a friend you have aikido tomorrow, and someone asks, "What's that?" you're not going to tell them it's the study of the spirit, because that could mean anything and he's going to have no idea what you're talking about. The word aikido
has to mean something more specific than that, or else it has no meaning at all.