Relating to a rib.
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cos·tal 'käs-təl adj of, relating to, involving, or situated near a rib <\costal fractures caused by violent coughing>
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adj.
of or relating to the ribs.
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cos·tal (kosґtəl) [L. costalis, from costa rib] pertaining to a rib or ribs.Medical dictionary. 2011.