Definition of "step in" []

• To act as a replacement or substitute. (verb)
• To get involved; to act (verb)

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• "Self-revelation is purported to be—perhaps demonstrated to be—the first step in self-actualization."
• "The final step in food processing is the addition of vitamins and minerals, to make up for what was lost during the initial heat-stripping phase."
• "The vital first step in that process was making a very precise burn called “LOI-1,” the basic Lunar Orbit Insertion."