# undetectable

/əndɪˈtɛktəbəɫ/ (US) · /ˌʌndɪtˈɛktəbəl/ (UK) · CEFR B2 · Adjective

Source: https://englishreference.com/word/undetectable
Updated: 2026-05-20

## Definition

so small or hidden that you cannot see, hear, or find it. You use this to describe things that are completely invisible or impossible to notice.

For teachers: impossible to perceive, identify, or measure by any known means. Often used to describe very low levels of a substance or a signal that is masked by background noise.

## Examples

- The virus is undetectable in the blood test.
- The new software allows the spy to remain undetectable even when the system is actively scanning for malware.
- The signal was so weak that it became undetectable by the receiver, making it impossible for the researchers to track the satellite's exact position.

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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.