According to a rule, principle, or norm; conforming to established law, order, habit, or usage; conforming with a certain type or standard; not abnormal; regular; natural.Serving to fix a standard; intended to set the standard: as, a normal school (see below).In music, standard or typical: as, normal pitch or tone, a pitch or tone of absolute acoustical value, which is used as a standard of comparison. See key, 7, and natural key (under key).In geometry, perpendicular: noting the position of a straight line drawn at right angles to the tangent-line of a curve, or to the tangent-plane of a surface, at the point of contact.Synonyms Regular, Ordinary, Normal. That which is regular conforms to rule or habit, and is opposed to that which is irregular, fitful, or exceptional. That which is ordinary is of the usual sort and excites no surprise; it is opposed to the uncommon or the extraordinary. That which is normal conforms or may be figuratively viewed as conforming to nature or the principles of its own constitution: as, the normal action of the heart; the normal operation of social influences; the normal state of the market.n. In geometry, a perpendicular; the straight line drawn from any point in a curve in its plane at right angles to the tangent at that point; or the straight line drawn from any point in a surface at right angles to the tangent-plane at that point. See cut under binomial.In chem.:Of a salt, having all the readily replaceable or basic hydrogen of the corresponding acid replaced by one or more metals or strongly electropositive radicals: distinguished from an acid salt in which this replacement is only partial.Of a solution for use in volumetric analysis, containing of the dissolved chemical substance the reactive equivalent of 1 gram of hydrogen in 1 liter of the solution at 16° C. See normal solution.n. The rule; the standard.n. In biology, a species or race considered as a fixed standard which individual organisms may approach by heredity and from which they may recede by variation.n. In meteorology, the average of a large number of observed values of any given meteorological element, for example, mean temperature, pressure, or rainfall for any hour of the day, or day of the year. The number of observations must be so large that a second group of the same number would give the same average or normal. The normals for the hours of local mean solar time may be corrected or adjusted so as to become normals for the hours of any other standard of time.n. In compar. psychol., an untrained or uninjured animal whose behavior is made the standard of reference for the interpretation of the conduct of other, trained or operated animals.