Often used in technical or abstract contexts to refer to the underlying force or cause that sets something in motion. Most commonly encountered in the compound 原動力 (げんどうりょく).
好奇心が彼の研究の原動だ。
Curiosity is the driving force behind his research.
この機械の原動は電気モーターです。
The motive power of this machine is an electric motor.
driving force; motive power
motor; engine
motorized bicycle; moped (under 50cc)
Compound of 原 (origin, source) and 動 (move). The exact historical derivation is uncertain, but the kanji suggest 'original movement' or 'source of motion'.