1. Pertaining to conforming to or consisting of a pattern, process, or standard regarded as usual or typical; regular; natural: Periodic rains are a normal weather condition at this time of year.
2. Physically, mentally, and emotionally healthy; the standard of performance in a given function or test, usually taken from the average or median achievement for the group concerned: The normal development of children includes phases of rapid physical growth as well as topsy turvy emotional adjustments as each individual seeks to understand his or her feelings.
3. Maintained or occurring in a natural status: High winds and sandstorms are normal occurrences on vast desert expanses.
4. In mathematics, descriptive of a line, or plane, that is perpendicular to another line or plane: The architect used a T-square to draw a normal line perpendicular to the cobblestones drawn on the plans to indicate where the gate in the garden should be located.
5. Etymology: from Late Latin normalis, "according to rule"; from Latin, "according to a square, forming a right angle"; from norma, "carpenter's square, pattern, rule"; believed to be from Greek gnomona, accusative of gnomon, "interpreter, discerner, pointer on a sundial, carpenter's square" + -alis, "-al"; a suffix that forms adjectives.

The etymological background of the term, normal

The basic sense of the noun "norm" is "an authoritative standard or model". This is derived from the Latin "norma" which means "rule or pattern" as well as "a carpenter's square", because a square provides a standard or rule which ensures that a carpenter can regularly reproduce corners and edges which are straight and that form right angles.

• The Latin adjective "normalis", formed from "norma", originally meant "forming a right angle" or "according to a square", and it is from this Latin sense that we get the earliest attested (established as genuine) sense of normal in English, which was "perpendicular".
• Latin "normalis", was also used in more extended senses, and by the Late Latin period, its usual meaning was "according to rule" and so it was that most of the meanings of the English word, normal, have been derived from this Late Latin usage.
• The Latin "norma", "carpenter's square", is thought by some linguists to be derived from Greek "gnomon", which also means "carpenter's square".
• Additional senses are "the pointer on a sundial", "interpreter", and "discerner".
• All of these meanings reflect in varying degrees the origin of the word in the verb "gignoskein", "to know".
• "Gnomon" was borrowed into English directly from Greek and is still used to mean "the style of a sundial" as well as other senses derived from or related to this.