# litmus

/ˈɫɪtməs/ (US) · /lˈɪtməs/ (UK)

Source: https://englishreference.com/word/litmus
Updated: 2026-08-27

## Senses

### 1. chemical dye

noun · CEFR C2 · Technical

a purple dye from plants that turns red in acid and blue in alkaline liquids.

For teachers: a water-soluble mixture of different dyes extracted from lichens, used as a pH indicator.

- The scientist extracted litmus from the lichen to create a new batch of testing solution.
- Litmus is primarily used to determine acidity or alkalinity, as its constituent chromophores undergo structural changes in response to protonation.

### 2. acidity test

noun · CEFR B2

a quick test using special paper to see if a liquid is an acid.

For teachers: a chemical test for acidity or alkalinity, typically performed using paper strips treated with the dye.

- We used a strip of litmus to check the pH level of the swimming pool water.
- The chemistry students performed a litmus test on various household liquids to observe the immediate color transition from blue to red.

### 3. a decisive indicator

noun · CEFR C1 · Academic

a simple way to judge someone's character or the success of a plan.

For teachers: a figurative indicator or test that relies on a single factor to provide a decisive evaluation of a situation or person.

- The way a person treats a waiter is often a litmus test for their true character.
- The candidate's stance on environmental regulation served as a litmus test for the party's more progressive wing during the primary elections.

Usage: Often used in the compound 'litmus test'.

## Examples

- The teacher used litmus paper to test the lemon juice.
- In the chemistry lab, students dipped blue litmus paper into the solution to confirm it was acidic.
- Before the advent of digital sensors, litmus served as the primary tool for determining the chemical nature of a substance, providing a simple visual cue for basic or acidic environments.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.