Normal /(nôr"mal)/

Nor·mal

Normal

a.
  1. According to an established norm, rule, or principle; conformed to a type, standard, or regular form; performing the proper functions; not abnormal; regular; natural; analogical.
    Deviations from the normal type.
  2. According to a square or rule; perpendicular; forming a right angle; as, a line normal to the base. Specifically: Of or pertaining to a normal. (Geom.)
  3. Standard; original; exact; typical. (Chem.)

Phrases & Compounds
Normal equations
a set of equations of the first degree equal in number to the number of unknown quantities, and derived from the observations by a specified process. The solution of the normal equations gives the most probable values of the unknown quantities.
Normal group
a group of rocks taken as a standard.
Normal place
the apparent place in the heavens of a planet or comet at a specified time, the place having been determined by a considerable number of observations, extending perhaps over many days, and so combined that the accidental errors of observation have largely balanced each other.
Normal school
a school whose methods of instruction are to serve as a model for imitation; an institution for the training of teachers.
Syn. -- Normal, Regular, Ordinary.

Regular and ordinary are popular terms of well-known signification; normal has now a more specific sense, arising out of its use in science. A thing is normal, or in its normal state, when strictly conformed to those principles of its constitution which mark its species or to the standard of a healthy and natural condition. It is abnormal when it departs from those principles.

Normal

n.
  1. Any perpendicular. (Geom.)
  2. A straight line or plane drawn from any point of a curve or surface so as to be perpendicular to the curve or surface at that point. (Geom.)