# infectious

/ˌɪnˈfɛkʃəs/ (US) · /ɪnfˈɛkʃəs/ (UK)

Source: https://englishreference.com/word/infectious
Updated: 2026-06-20

## Senses

### 1. medical/disease

adjective · CEFR B2 · Technical

describes a disease that can be passed from one person to another through germs or viruses.

For teachers: relating to a disease caused by a pathogen that enters the body and is capable of being transmitted to other hosts.

- The doctor warned that the flu is highly infectious during the first few days.
- Public health officials monitored the outbreak closely, concerned by how infectious the new strain appeared to be in densely populated urban areas.

### 2. spreading feelings

adjective · CEFR B2

describes a feeling or behavior, like a laugh or a smile, that quickly spreads to other people.

For teachers: tending to spread from person to person through social contact or emotional resonance.

- Her infectious laugh soon had everyone in the room giggling along with her.
- The team captain's infectious enthusiasm served as a catalyst for the younger players, lifting their spirits despite the early deficit in the score.

### 3. exciting or memorable

adjective · CEFR C1 · Informal

describes something very exciting or catchy that makes people want to join in.

For teachers: evoking excitement or interest in a way that is easily picked up by an audience or group.

- The band played a song with an infectious beat that got everyone dancing.
- The marketing campaign relied on an infectious energy that resonated with younger consumers, leading to a rapid increase in brand recognition.

## Examples

- Her laughter is infectious and makes everyone in the room smile.
- The doctor warned that the flu is highly infectious during the first few days of symptoms.
- Despite the grim economic forecast, the CEO maintained an infectious optimism that eventually permeated the entire management team and revitalized the project.

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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.