Plural noun: thin mortar used between tiles or in cracks; Third person singular verb: to fill or seal with grout.
From Old English 'grut,' meaning 'sediment' or 'lees,' possibly related to 'grout' meaning porridge. The construction material use emerged in the 19th century as the word was applied to the thin filling material.
Grout seems boring, but it's actually crucial engineering—without proper grout between tiles, water infiltrates and destroys entire walls, so this humble mud-paste prevents millions of dollars in property damage annually.
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