Source : Webster's Revised Unabridged Dictionary (1913)

      12 seconds ('') make 1 inch or prime. 12 inches or primes
      (') make 1 foot.                            --B.
                                                  Greenleaf.

   Note: The meter, the accepted scientific standard of length,
         equals 39.37 inches; the inch is equal to 2.54
         centimeters. See {Metric system}, and {Meter}.

   2. A small distance or degree, whether of time or space;
      hence, a critical moment.

            Beldame, I think we watched you at an inch. --Shak.

   {By inches}, by slow degrees, gradually.

   {Inch of candle}. See under {Candle}.

   {Inches of pressure}, usually, the pressure indicated by so
      many inches of a mercury column, as on a steam gauge.

   {Inch of water}. See under {Water}.

   {Miner's inch}, (Hydraulic Mining), a unit for the
      measurement of water. See {Inch of water}, under {Water}.

Source : WordNet®

by inches
     adv : by a short distance; "they moved it by inches" [syn: {little
           by little}, {by small degrees}]