An Etymological Dictionary of Astronomy and Astrophysics

A quantity or dimension adopted as a standard of measurement.
Math.: The lowest positive natural number.
The first digit to the left of the decimal point in decimal notation, representing a whole number less than ten.
An element in a ring that has a multiplicative inverse.

Etymology (EN): Back formation from → unity.

Etymology (PE): Yekâ, yekân, from yek, → one.