# similarity

Pronunciation: US say "sim-uh-LAIR-uh-tee" /ˌsɪm.əˈlɛɹ.ə.ti/; UK say "sim-i-LA-ri-tee" /ˌsɪm.ɪˈlæɹ.ɪ.ti/; AUS say "sim-uh-LA-ruh-tee" /ˌsɪm.əˈlæɹ.ə.ti/

## Noun

1. The quality of looking very much like something else.
   - Simple: How much one thing looks like another.
   - _The similarity between the forged painting and the original fooled several experts._
   - _Witnesses commented on the striking similarity in the two brothers' appearance._
2. The relation that holds between things which share one or more properties.
   - Simple: The fact that two or more things share some of the same features.
   - _Philosophers disagree about whether similarity reduces to shared properties or counts as a basic relation._
   - _Biological classification often rests on the similarity among organisms' genetic traits._
3. In geometry, a mapping of Euclidean space under which angles stay the same and every distance is scaled by one common factor.
   - Simple: A change that makes a shape bigger or smaller without changing its angles.
   - _Every similarity maps a figure onto another with the same shape but a different size._
   - _Composing two similarities always produces another similarity._
4. The property holding between two matrices when one can be obtained from the other through a change of basis.
   - Simple: When two matrices describe the same change, just written in different ways.
   - _The similarity of two matrices guarantees they share the same eigenvalues._
   - _To prove similarity, you find an invertible matrix that turns one into the other._

## Origin

From French "similarité," and formed morphologically from "similar" plus the suffix "-ity."

Source: DictionaryAI, https://dictionaryai.com/define/similarity (written from Wiktionary data, CC BY-SA 4.0: https://creativecommons.org/licenses/by-sa/4.0/).