semirecta

From semi- +‎ recta.

• IPA^(key): (Central, Balearic) [ˌsɛ.miˈrɛk.tə]
• IPA^(key): (Valencia) [ˌse.miˈrɛk.ta]

semirecta f (plural semirectes)

1. ray, half-line

• “semirecta”, in Diccionari de la llengua catalana [Dictionary of the Catalan Language] (in Catalan), second edition, Institute of Catalan Studies [Catalan: Institut d'Estudis Catalans], April 2007
• “semirecta” in termcat, Centre de Terminologia, 2026.

From sēmi- (“half”) +‎ rēcta (“straight line”). The term is attested in early modern scientific manuscripts (e.g. in the Galileo codices, see References) and is used in modern Latin to distinguish the geometric concept from radius.

• (Classical Latin) IPA^(key): [seː.mɪˈreːk.ta]
• (modern Italianate Ecclesiastical) IPA^(key): [se.miˈrɛk.ta]

sēmirēcta f

1. (New Latin, geometry) ray, half-line; a part of a line starting at a point and extending infinitely in one direction.

   Sēmirēcta ab $A$ in infinitum prōdūcitur.

   The ray is produced from A to infinity.

• **Historical usage**: The term appears in indexes of early modern scientific texts, such as the Galileo manuscripts.
• **Modern usage**: In contemporary mathematical Latin, it is used to strictly distinguish a "ray" (infinite in one direction) from a radius (finite segment from center to circumference).

First-declension noun.

• radius (classical usage)

• līnea
• rēcta
• sēgmentum

•Word sources

• “Index of Latin Words: semirecta”, in Galileo Prototype‎^[1], Max Planck Institute for the History of Science, 9 December 2025 (last accessed)