noun

penumbra

puh-NUM-bruh

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Penumbra (noun) means a partially shaded area around the edge of a full shadow, such as the one seen during an eclipse. Example: “As the eclipse progressed, the moon's penumbra swept slowly across the valley.”

noun

A partially shaded area around the edge of a full shadow, such as the one seen during an eclipse.

"As the eclipse progressed, the moon's penumbra swept slowly across the valley."

"Stand in the penumbra and you get some daylight, but not full sun."

"The tree cast a penumbra of soft grey light around its dark central shadow."

astronomy In astronomy, the lighter ring around the edge of a sunspot, which is darker than the sun's surface but paler than the sunspot's centre.

"Solar astronomers measured the width of the sunspot's penumbra."

"The penumbra fades gradually into the surrounding brightness of the sun."

medicine In medicine, the area of the brain after a stroke that has lost part of its blood supply and its function, while remaining structurally intact.

"Doctors hoped that blood flow could still be restored to the penumbra before it died off completely."

"Scans showed a penumbra surrounding the core of the stroke."

How to use penumbra

Learner’s notes

In plain EnglishThe soft, partly shaded edge around a proper shadow.

When to use it

It is a fairly technical word, most at home in astronomy, medicine or careful descriptive writing.

Memory tip

Remember the Latin roots: paene means 'almost', so a penumbra is 'almost' a shadow, not a full one.

Trace the full origin ↓

Easily confused with

umbra

Common pairings

cast a penumbra the penumbra of a shadow ischaemic penumbra penumbra of a sunspot

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C2 · Advanced serendipity Fortunate discoveries made entirely by accident.

Gen Z slang rizz Charm — the ability to attract a romantic interest.

B2 · Intermediate empathy The capacity to share another person’s feelings.

C1 · Advanced nonchalant Casually calm and relaxed; unconcerned.

Internet slang delulu Delusional — believing something against the odds.

Etymology nostalgia Greek nostos “return home” + algos “pain”.

C2 · Advanced serendipity Fortunate discoveries made entirely by accident.

Gen Z slang rizz Charm — the ability to attract a romantic interest.

B2 · Intermediate empathy The capacity to share another person’s feelings.

C1 · Advanced nonchalant Casually calm and relaxed; unconcerned.

Internet slang delulu Delusional — believing something against the odds.

Etymology nostalgia Greek nostos “return home” + algos “pain”.

Test yourself on “penumbra” A quick quiz — meaning, synonyms & usage →

Fill the gap

Can you complete this real example?

As the eclipse progressed, the moon's _____ swept slowly across the valley.

Etymology

Penumbra comes from New Latin pēnumbra. It was built from the Latin paene, meaning 'almost', joined to umbra, meaning 'shadow'.

Origin: Latin

Frequently asked questions

What does penumbra mean?

It is the partly shaded area at the edge of a shadow, such as the fringe of shade around an eclipse.

Is a penumbra lighter or darker than a full shadow?

Lighter. The penumbra is only partly blocked from the light source, unlike the fully dark shadow at its centre.

Why do astronomers and doctors both use the word penumbra?

Both borrow the same shadow imagery: astronomers use it for the paler edge of a sunspot, and doctors use it for the partly affected brain tissue around a stroke.

What is the meaning of penumbra?

"penumbra" (noun) means a partially shaded area around the edge of a full shadow, such as the one seen during an eclipse.