first base

  1. the base to the left of the pitcher, the first of the four bases that a base runner attempts to reach safely
  2. the defensive position played by the first baseman

See first base in American Heritage Dictionary 4

noun
  1. Baseball
    a. The first of the bases in the infield, counterclockwise from home plate.
    b. The fielding position occupied by the first baseman.
  2. Slang The first stage or step toward completion or success: “He never got to first base with any of his big wheels and deals” (Ross Macdonald).

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