AIKIDO (in Japanese 合気道, in Hepburn's transcription Aikidō*) is a relatively recent Japanese martial art that was developed in 1920-ies. Morihei Ueshiba (O-Sensei), having previously been trained by different budo masters, developed and synthesized this new type of martial art. In aikido one focuses on exploiting the "attacker's" force and gradually getting rid of the image of the opponent and the need of bringing him under.
The word aikidō could be translated as a path that leads to harmony or a harmonizing path.
* the diacritical sign over the letter 'o' designates that it should be pronounced as a long vowel.