01 a. Acting of or by one's self or by itself; -- said especially of a machine or mechanism which is made to perform of or for itself what is usu…
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Acting of or by one's self or by itself; -- said especially of a machine or mechanism which is made to perform of or for itself what is usually done by human agency; automatic; as, a self-acting feed apparatus; a self-acting mule; a self-acting press.