In Martial Arts & related idea-worlds Aiki has following meanings:
- Inner Strength,
Aiki is also 'work', 'practice', 'training'.
Aiki in Martial Arts is also 'pulling when enemy pushes & pushing when enemy pulls' - using enemy's strength & momentum against him, to defeat with the minimal force use.
It's also 'blending in combat without clashing', finding optimal distance & position to strike - there are also methods to unbalance enemy's body & mind.
This goes well with Atemi, as one can strike, pressure or bend vital points or body parts to lead enemy's body as Martial Artist needs to win. For example by bending a joint, throwing enemy on ground, then finishing with a strike at a vital part.
Use of inner strength (ki) may involve the use of breathing coordinated with movement. This natural power can be produced when body and consciousness (mind) are unified.
Smaller, with more fragile bodies, weaker (muscles-wise, but not training-wise) Martial Artists can win against much larger, heavier or stronger-muscled enemies that way. This is good news for women as well, i think.
Greater practice with Martial Arts allows to defeat enemies without killing as well.