# penicillin

/ˌpɛnəˈsɪɫən/ (US) · /pˈɛnɪsˌɪlɪn/ (UK)

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

## Senses

### 1. medicine

noun · CEFR B2

a type of medicine called an antibiotic that kills bacteria and treats many common illnesses.

For teachers: a group of antibiotics derived from Penicillium moulds, used to treat various bacterial infections by inhibiting cell wall synthesis.

- The doctor gave him penicillin to help clear up his chest infection.
- The discovery of penicillin revolutionised modern medicine, providing a powerful tool against previously fatal bacterial diseases.

### 2. the mould

noun · CEFR C1 · Technical

the specific type of blue-green mould that scientists use to make the medicine.

For teachers: a fungus of the genus Penicillium that produces the antibiotic substance.

- Alexander Fleming noticed that a specific penicillin mould was killing the bacteria in his lab.
- Researchers isolated the active compound from the penicillin mould to develop the first mass-produced antibiotic.

## Examples

- The doctor gave me penicillin for my ear infection.
- Since the patient was allergic to penicillin, the medical team had to find an alternative antibiotic for the surgery.
- The mass production of penicillin during the mid-twentieth century fundamentally altered the landscape of modern medicine, turning previously fatal infections into manageable conditions.

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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.