semirecta

Catalan

Etymology

From semi- +‎ recta.

Pronunciation

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

Noun

semirecta f (plural semirectes)

1. ray, half-line

Further reading

• “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.

Latin

Etymology

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.

Pronunciation

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

Noun

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.

Usage notes

• **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).

Declension

First-declension noun.

	singular	plural
nominative	sēmirēcta	sēmirēctae
genitive	sēmirēctae	sēmirēctārum
dative	sēmirēctae	sēmirēctīs
accusative	sēmirēctam	sēmirēctās
ablative	sēmirēctā	sēmirēctīs
vocative	sēmirēcta	sēmirēctae

Synonyms

• radius (classical usage)

Related terms

• līnea
• rēcta
• sēgmentum

References

•Word sources

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