ζ | zeta

The Greek letter ζ (zeta) was derived from the ancient Phoenician letter 𐤆 (zayin) which meant “sword” or some other weapon.

In the system of Greek numerals, the letters α to ε have the respective values 1 through 5. Bizarrely, ζ has the value of 7. This may account for the fact that chemists don’t like using Greek letters beyond ε when numbering the atoms in the chain. Still, the lower-case letter ζ has some uses in maths and sciences, for example:

• in colloidal chemistry: ε_i, ζ-potential, the electrokinetic potential of colloidal dispersions
• in mathematics: ζ(s), the Euler–Riemann zeta function
• in mathematics: ζ(z; Λ), the Weierstrass zeta function
• in pharmacology: ζ-opioid receptor, aka opioid growth factor receptor

More photos related to letters, numbers and sea glass @ Shutterstock.