# penumbra

/pɪˈnəmbɹə/ (US) · /pˈɛnʌmbɹɐ/ (UK) · CEFR C2 · Noun

Source: https://englishreference.com/word/penumbra
Updated: 2026-04-24

## Definition

the lighter outer part of a shadow where only some of the light is blocked. You also use it to describe a secondary area or a group of things related to a central topic.

For teachers: the partially shaded outer region of a shadow cast by an opaque object; a peripheral or marginal area where something exists to a lesser degree. Countable.

## Examples

- The moon moves into the penumbra during the early stages of the eclipse.
- We could barely see the outlines of the trees standing in the penumbra of the streetlamp.
- The legal ruling affects not only the direct participants but also an entire penumbra of related industries that rely on current intellectual property definitions for their operations.

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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.