Rho (letter)

Rho (letter)

Rho (uppercase Ρ, lowercase ρ or Unicode|ϱ) is the 17th letter of the Greek alphabet. In the system of Greek numerals it has a value of 100. It is derived from Semitic Rêš "head" (see Resh). Its uppercase form is not to be confused with the Roman letter P.

Rho is generally classed as a liquid (together with lambda and sometimes the nasals mu and nu), which has important implications for morphology. It is pronounced similarly to the letter "r" in languages with a Latin-derived alphabet. In polytonic orthography a rho at the beginning of a word is conventionally written with a rough breathing (equivalent to "h") — polytonic|ῥ — and a double rho within a word is written with a smooth breathing over the first rho and a rough breathing over the second — polytonic|ῤῥ — apparently reflecting an aspirated or voiceless pronunciation in Ancient Greek, hence the various Greek-derived English words which start with "rh" or contain "rrh". The name of the letter is written in Greek as Unicode|ῥῶ (polytonic) or ρω/ρο (monotonic).

Letters that arose from rho include Roman R and Cyrillic Er (Р).

Common notational uses

The characters Ρ, ρ and Unicode|ϱ are also used outside its Greek alphabetical context in Science, and Mathematics.

*In Physics
**to represent Density (ρ)
**to represent Resistivity (ρ)

*In Mathematics
**to represent the Radius in a system of spherical polar coordinates
**to represent the correlation coefficient of a population parameter
**to represent the Spectral radius of a matrix A denoted as ho(A)
**to represent a Plastic number

*In Economics to represent the discount rate of future pence cash flows

*In Molecular Biology to represent the Rho protein responsible for termination of RNA synthesis. In such occasions, it is often represented as unicode|ϱ ("rho symbol" U+03F1), to avoid confusion with the Latin letter "p"

*In Programming
**For LaTeX, the symbols are P (Ρ), ho ( ho), and varrho (varrho)
**The lower-case rho "ρ" has a special meaning in the APL programming language

See also

*Р, р - Er (Cyrillic)
*П, п - Pe (Cyrillic)
*R, r - Latin
*P, p - Latin

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Rho — may refer to: NOTOC *Rho (letter), a letter of the Greek alphabet, upper case Ρ, lower case ρymbols;in mathematics * Spectral radius in a spherical coordinate system;in physics * Density of a material * Volume charge density * Resistivity of a… …   Wikipedia

  • Rho — Das Rho (griechisches Neutrum Ρω, Majuskel Ρ, Minuskel ρ oder ϱ) ist der 17. Buchstabe des griechischen Alphabets und hat nach dem milesischen Prinzip einen numerischen Wert von 100. Am Anfang eines altgriechischen Wortes ist es immer… …   Deutsch Wikipedia

  • rho|ta|cism — «ROH tuh sihz uhm», noun. an excessive use, mispronunciation, or substitution of the sound represented by r in English. ╂[< New Latin rhotacismus < Greek rhōtakízein overuse the letter rhô rho] …   Useful english dictionary

  • rho — [rō] n. [Gr rhō < Sem: cf. Heb rosh] the seventeenth letter of the Greek alphabet (Ρ, ρ) …   English World dictionary

  • rho — ► NOUN ▪ the seventeenth letter of the Greek alphabet (P, ), transliterated as ‘r’ or ‘rh’. ORIGIN Greek …   English terms dictionary

  • rho|dop|sin — «roh DOP sihn», noun. a purplish red protein pigment that is sensitive to light, found in the rods of the retina of the eye; visual purple: »Rhodopsin was found to be the visual pigment in all vertebrates from the primitive lamprey to man… …   Useful english dictionary

  • Rho Psi — The Rho Psi Society (ΡΨ) is an honorary fraternity Greek letter fraternity. Although founded as a student society, it is no longer active at the collegiate level. The objectives of the Society are to promote and perpetuate friendship among… …   Wikipedia

  • rho — /roh/, n., pl. rhos. 1. the 17th letter of the Greek alphabet (P). 2. the consonant sound represented by this letter. [1350 1400; ME < Gk rhô] * * * …   Universalium

  • letter — I (New American Roget s College Thesaurus) n. character, symbol; cuneiform, hieroglyphic; capital, majuscule; small letter, minuscule; consonant, vowel, digraph, diphthong; missive, note. See writing, communication. II (Roget s IV) n. 1. [A unit… …   English dictionary for students

  • letter of the alphabet — noun the conventional characters of the alphabet used to represent speech his grandmother taught him his letters • Syn: ↑letter, ↑alphabetic character • Derivationally related forms: ↑letter (for: ↑letter) …   Useful english dictionary

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.