Normal
mid 17th century (in the sense ‘right-angled’): from Latin normalis, from norma ‘carpenter's square’ (see norm). Current senses date from the early 19th century.
wiktionary
From Latin normālis(“made according to a carpenter's square; later: according to a rule”), from nōrma(“carpenter's square”), of uncertain origin. [1] [2] [3] [4] The earliest use of the word in English was to mean "perpendicular; forming a right angle" like something normālis(“made according to a carpenter's square”), [1] [5] but by Late Latin normālis had also come to mean "according to a rule", from which modern English senses of the word derive: [5] in the 1800s, as people began to quantitatively study things like height and weight and blood pressure, the usual or most common values came to be referred to as "normal", and by extension values regarded as healthy or desirable came to be called "normal" regardless of their usuality. [6]
etymonline
normal (adj.)
c. 1500, "typical, common;" 1640s, in geometry, "standing at a right angle, perpendicular," from Late Latin normalis "in conformity with rule, normal," in classical Latin "made according to a carpenter's square," from norma "rule, pattern," literally "carpenter's square," a word of unknown origin (see norm). Meaning "conforming to common standards or established order or usage, regular, usual" is attested from 1828 but probably is older than the record [Barnhart].
Meaning "heterosexual" is by 1914. As a noun meaning "usual state or condition," from 1890 (in geometry as "a perpendicular" from 1727). Sense of "a normal person or thing" is attested by 1894. Normal school "training college for teachers" (1835) is a translation of French école normale (1794), a creation of the French Republic; the notion is of "serving to set a standard." The U.S. city of Normal, Illinois, was named 1857 for the normal school established there.
