The quality or state of being capillary; the extent to which something exhibits capillary properties.
From capillary (Latin capillaris 'hair-like') plus the noun-forming suffix -ness, which converts adjectives into abstract nouns describing a quality or state.
The capillariness of a material determines whether it will soak up liquids or repel them—it's why some fabrics are super absorbent while others are water-resistant!
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