penetrable

Something can be called penetrable if substances can pass through it. A coffee filter is penetrable, for example, because it allows water to drip through it.

Your curtains are penetrable if they let sunlight peek through, and a country's borders are considered penetrable if they allow people to pass through them unnoticed by guards or customs officials. In basketball, having a penetrable defense is bad news — it means it allows the opposition's players to get right up to the basket, where they can easily shoot. Sometimes penetrable means "understandable," as in a penetrable poem or penetrable song lyrics.

Definitions of penetrable
1

adj admitting of penetration or passage into or through

“a penetrable wall”
penetrable defenses”
Antonyms:
impenetrable
not admitting of penetration or passage into or through
dense, thick
hard to pass through because of dense growth
show more antonyms...

adj capable of being penetrated

penetrable defenses”
Synonyms:
vulnerable
susceptible to attack

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