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square one

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noun
  1. a starting point; initial stage or step: If this plan fails, we'll have to go back to square one.

Origin of square one

First recorded in 1955–60; alluding to board games in which a player is penalized by being forced to return to the starting point
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Related Words for square one

beginning, outset