radius

radi-us Stab; Speiche; Strahl

Of uncertain origin. Some connect it with rādīx and rāmus. Tucker suggests Proto-Indo-European *neredʰ- (“extend forth, rise, outward”) akin to Sanskrit वर्धते (vardhate, “rise, grow”), or from Ancient Greek ἄρδις (árdis, “sharp point”).May ultimately be from Proto-Indo-European *reh₁t- (“bar, beam, stem”).

Pronunciation

• (Classical Latin) IPA^(key): [ˈra.di.ʊs]
• (modern Italianate Ecclesiastical) IPA^(key): [ˈraː.d̪i.us]

Noun

radius m (genitive radiī or radī); second declension

1. a staff, rod
   1. a spoke of a wheel
   2. a rod for measurement
   3. the radius of a circle; a rotating radial arm
   4. (weaving) a shuttle
   5. (poetic) a bolt or shaft
   6. the spur of a bird's leg
   7. the tail-spine of a stingray
   8. (anatomy) the radius (the outer bone of a forearm)
2. a ray of light (also reflected)
   1. (according to an ancient theory of vision) a ray extending from the eye to the object seen
3. the name of an elongated variety of olive
4. the name of a rod with which geometers make figures in dust, also known as a virga

Declension

Second-declension noun.

	singular	plural
nominative	radius	radiī
genitive	radiī radī1	radiōrum
dative	radiō	radiīs
accusative	radium	radiōs
ablative	radiō	radiīs
vocative	radie	radiī

¹Found in older Latin (until the Augustan Age).