English calls the moon a measurer — the Germanic root *mēnô is kin to 'month,' an old tool for counting seasons. Spanish luna and Esperanto luno reach instead toward light: both trace to PIE *leuk-, the root that brightens 'lucid' and 'luminous.' The Chinese 月 bypasses both — it is simply a drawn crescent, essentially unchanged since Shang scribes pressed it into oracle bone. Three strategies — the functional, the luminous, the pictorial — for one indifferent silver disc.
The same PIE root (*meh₁-, to measure) yielded Latin mēnsis (month), Greek μήν (mḗn, month), and Sanskrit māsa. English 'month,' 'menstruation,' and 'moon' are distant cousins from one root idea: the celestial accountant.
Latin lūna entered Spanish unchanged in form. The word seeded English borrowings 'lunar,' 'lunacy,' and 'lunatic' — the moon as presumed cause of madness. Grammatically feminine in Spanish, a gender shared with the moon goddesses Luna, Selene, and Artemis of antiquity.
Originally an oracle-bone pictogram of a crescent moon: the curved outer strokes trace the lit edge of the waxing or waning disc. The two interior lines were added as writing formalized from oracle bone through bronze script to seal script — they reflect scribal convention, not additional meaning. The crescent silhouette has remained recognizable for over three thousand years.
月 doubles as the word for 'month' (一月 = January, lit. 'first month'). Key compounds: 月光 (yuèguāng, moonlight), 月亮 (yuèliàng, the colloquial moon — literally 'moon-bright'), 月圆 (yuèyuán, full moon — 'moon-round').
Productive derivations: lunlumo (moonlight; lun- + lumo 'light'), plenlumo (full moon; plen- 'full' + lumo), duonluno (half-moon; duon- 'half' + luno). Zamenhof drew heavily on Romance and Germanic roots; luno is squarely Romance.
We look at the same disc, and one language reaches for its ruler, another for its lamp, another for its silhouette — and somewhere, an ancient hand simply drew a crescent and called it done.