porous

American  

[pawr-uhs, pohr-] / ˈpɔr əs, ˈpoʊr- /

adjective

1. full of pores.

2. permeable by water, air, etc.

   Synonyms:

   riddled, sievelike, pervious, penetrable

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porous British  

/ ˈpɔːrəs /

adjective

1. permeable to water, air, or other fluids

2. biology geology having pores; poriferous

3. easy to cross or penetrate

   the porous border into Thailand

   the most porous defence in the league

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porous Scientific  

/ pôr′əs /

1. Having many pores or other small spaces that can hold a gas or liquid or allow it to pass through.

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Other Word Forms

• nonporous adjective
• nonporousness noun
• porously adverb
• porousness noun
• unporous adjective
• unporousness noun

Etymology

Origin of porous

First recorded in 1350–1400; Middle English, variant of porose, from Medieval Latin porōsus; see pore ², -ous

Explanation

If something is full of tiny holes or openings, you can describe it as porous. A sponge is porous, and if the border between countries is open for anyone to cross easily, it too can be called porous. You can see the word pore — meaning "a tiny opening" — in porous. When potters make a mug, they use special glazes to seal the porous clay, which otherwise would absorb the liquid you put in the mug. This meaning has expanded so porous can describe any barrier that allows easy passage in and out, like the porous border between two countries that allows residents to move easily between them.

Example Sentences

Chalk streams emerge from springs in porous chalk bedrock, which acts as a filter to remove sediment, characterised by beautifully clear water and a gravelly bottom.

From BBC • Mar. 8, 2026

They’re porous defensively and have a boring, predictable offense largely consisting of alternating one-on-one isolations between their “Big Three” most every trip down the court.

From Los Angeles Times • Feb. 28, 2026

To use as a metal, titanium ore has to be turned into a porous form called sponge — the U.S. imports over 95% of that.

From MarketWatch • Feb. 12, 2026

The border in the area is porous and poorly demarcated, which contributed to Lebanese nationals settling in Syria and facilitated the smuggling for which the region is known.

From Barron's • Feb. 5, 2026

But the frame was the original porous stone used to build the manor.

From "Artemis Fowl" by Eoin Colfer