to become solid or hard; to make something more firm, stable, or certain.
From 'solid' (Latin 'solidus,' meaning firm or compact) plus '-fy' (Latin suffix meaning to make). The term became common in scientific English in the 1700s.
Water is unusual because it expands when it solidifies into ice—most substances shrink when freezing, which is why icebergs float and nearly destroyed the Titanic!
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