Definition of start in onchiefly US, informal
- She started in on another book.
- My dad started in on me about not having a job.
: to move suddenly and violently : spring
: to react with a sudden brief involuntary movement
: to issue with sudden force
: a sudden involuntary bodily movement or reaction
: a brief and sudden action or movement
: a sudden capricious impulse or outburst
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