1. Conforming with, adhering to, or constituting a norm, standard, pattern, level, or type; typical: normal room temperature; one's normal weight; normal diplomatic relations.
2. Biology. Functioning or occurring in a natural way; lacking observable abnormalities or deficiencies.
3. (Abbr. n or N) Chemistry.
   1. Designating a solution having one gram equivalent weight of solute per liter of solution.
   2. Designating an aliphatic hydrocarbon having a straight and unbranched chain of carbon atoms.
4. Mathematics.
   1. Being at right angles; perpendicular.
   2. Perpendicular to the direction of a tangent line to a curve or a tangent plane to a surface.
5. 1. Relating to or characterized by average intelligence or development.
   2. Free from mental illness; sane.

1. Something normal; the standard: scored close to the normal.
2. The usual or expected state, form, amount, or degree.
3. 1. Correspondence to a norm.
   2. An average.
4. Mathematics. A perpendicular, especially a perpendicular to a line tangent to a plane curve or to a plane tangent to a space curve.

[Middle English, from Late Latin normālis, from Latin, made according to the square, from norma, carpenter's square.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.