1. A measure of length, the twelfth part of a foot, commonly subdivided into halves, quarters, eights, sixteenths, etc., as among mechanics. It was also formerly divided into twelve parts, called lines, and originally into three parts, called barleycorns, its length supposed to have been determined from three grains of barley placed end to end lengthwise. It is also sometimes called a prime (′), composed of twelve seconds (′′), as in the duodecimal system of arithmetic. [ 1913 Webster ]

The symbol ′ is the same symbol as the light accent, or the "minutes" of an arc. The "seconds" symbol should actually have the two strokes closer than in repeated "minutes", but in this dictionary ′′ will be interpreted as "seconds". [ PJC ]

12 seconds (′′) make 1 inch or prime. 12 inches or primes (′) make 1 foot. B. Greenleaf. [ 1913 Webster ]

☞ 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. [ 1913 Webster ]

2. A small distance or degree, whether of time or space; hence, a critical moment; also used metaphorically of minor concessins in bargaining; as, he won't give an inch; give him an inch and he'll take a mile. [ 1913 Webster ]

Beldame, I think we watched you at an inch. Shak. [ 1913 Webster ]

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. [ 1913 Webster ]

1. To drive by inches, or small degrees. [ R. ] [ 1913 Webster ]

He gets too far into the soldier's grace
And inches out my master. Dryden. [ 1913 Webster ]

2. To deal out by inches; to give sparingly. [ R. ] [ 1913 Webster ]

With slow paces measures back the field,
And inches to the walls. Dryden. [ 1913 Webster ]

Inch stuff, boards, etc., sawed one inch thick. [ 1913 Webster ]