# phi

> English word · Noun · IPA /faɪ/ · frequency rank #13,979

## Definitions
1. Φ, the 21st letter of the Euclidean and modern Greek alphabet, usually romanized as "ph".
2. The golden ratio.
3. A visual illusion whereby a sequential pattern of lights produces a false sense of motion.

## Etymology
From Late Latin phi, from Ancient Greek φεῖ (pheî).

## Easily confused with
- **PM** (https://plainspell.com/en/vs/phi-vs-pm)
- **PP** (https://plainspell.com/en/vs/phi-vs-pp)
- **PR** (https://plainspell.com/en/vs/phi-vs-pr)
- **pt** (https://plainspell.com/en/vs/phi-vs-pt)
- **PS** (https://plainspell.com/en/vs/phi-vs-ps)
- **po** (https://plainspell.com/en/vs/phi-vs-po)
- **pi** (https://plainspell.com/en/vs/phi-vs-pi)
- **PL** (https://plainspell.com/en/vs/phi-vs-pl)
- **PU** (https://plainspell.com/en/vs/phi-vs-pu)
- **PK** (https://plainspell.com/en/vs/phi-vs-pk)
- **PV** (https://plainspell.com/en/vs/phi-vs-pv)
- **PJ** (https://plainspell.com/en/vs/phi-vs-pj)
- **PW** (https://plainspell.com/en/vs/phi-vs-pw)
- **PX** (https://plainspell.com/en/vs/phi-vs-px)
- **put** (https://plainspell.com/en/vs/phi-vs-put)
- **pro** (https://plainspell.com/en/vs/phi-vs-pro)
- **pop** (https://plainspell.com/en/vs/phi-vs-pop)
- **pot** (https://plainspell.com/en/vs/phi-vs-pot)
- **pin** (https://plainspell.com/en/vs/phi-vs-pin)
- **pit** (https://plainspell.com/en/vs/phi-vs-pit)

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/phi