Rho (letter)

Rho (/ˈroʊ/; uppercase Ρ, lowercase ρ or ϱ; Greek: ῥῶ) is the 17th letter of the Greek alphabet. In the system of Greek numerals, it has a value of 100. It is derived from Phoenician letter res . Its uppercase form is not to be confused with the Latin letter P, although both types use the same glyph: P.

Rho is classed as a liquid consonant (together with lambda and sometimes the nasals mu and nu), which has important implications for morphology. In both Ancient and Modern Greek, it represents a trilled or tapped r.

In polytonic orthography a rho at the beginning of a word is written with a rough breathing (equivalent to h) — ῥ rh — and a double rho within a word is written with a smooth breathing over the first rho and a rough breathing over the second — ῤῥ rrh — apparently reflecting an aspirated or voiceless pronunciation in Ancient Greek, hence the various Greek-derived English words that start with rh or contain rrh.

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