Seis

Seis is the Spanish and Portuguese word for the number six. It is used in counting and in everyday language to denote the quantity of six items, years, days, hours, dates, and other measurements. In phrases such as seis días (six days) or seis de julio (the sixth of July), the word functions as the cardinal number. The term appears across various contexts in Spanish- and Portuguese-speaking regions, reflecting the common Roman-numeral-based counting system shared with many Romance languages.

Etymology and cognates: Seis derives from the Latin word sex, the ancestor of the number six in many Romance languages. Related forms include Italian sei, French six, and Romanian șase, all tracing back to the same root. The similarity among these words reflects a shared linguistic history within the Romance language family.

In science and technology: SEIS, an acronym for Seismic Experiment for Interior Structure, refers to a seismometer onboard NASA’s InSight lander on Mars. Launched in 2018 and deployed on the Martian surface, SEIS was designed to measure quakes and other seismic phenomena to improve understanding of Mars’ internal structure. The instrument has contributed data on Martian interior layering and crustal properties, supporting planetary science research.

In addition to these uses, seis may appear in proper names, titles, or cultural references in Spanish- and Portuguese-speaking contexts, where it generally retains its meaning as the number six.