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

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

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

There were outdoor hallways, planted patios, a sculpted and porous internal courtyard, and even a new “paseo” next door — a closed street turned into a lovely space for farmers markets and other gatherings.

From Los Angeles Times • Jun. 18, 2026

Congolese mining towns tend to be porous and migrant-heavy, rough, difficult places to live in some of the country’s roughest, most difficult areas, where there is plenty of reason to distrust outsiders.

From Slate • Jun. 9, 2026

The planned centres in West Bengal have drawn particular concern because of the state's porous border with Bangladesh and its long history of migration.

From Barron's • May 25, 2026

As that happens, the porous rock temporarily locks up, slowing or stopping the rupture before it can continue spreading and becoming larger.

From Science Daily • May 16, 2026

Slag looks like pieces of porous rock but actually is the cinders left over when iron ore is melted down to make steel.

From "Flying to the Moon: An Astronaut's Story" by Michael Collins