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

The forests are dense and the region's porous borders make it easy for the militants to set up bases and to move across countries without being detected by the security forces.

From BBC • Apr. 9, 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

Particles emitted from a fusion plasma will erode the reactor wall, contaminating the plasma and rendering most known materials brittle and porous within months.

From The Wall Street Journal • Dec. 28, 2025

The border between their lands was porous; the Queen’s death would hover over their cities and villages, too.

From "Huntress" by Malinda Lo