The quality of being stiff, hard, and not flexible, or the quality of being very strict and unwilling to change.
From Latin 'rigidus' (stiff), possibly related to 'rigere' (to be stiff or numb). The metaphorical meaning (inflexibility of rules or thinking) developed in the 1600s.
Scientists discovered that too much rigidity in a material makes it brittle and prone to shattering, but too much flexibility makes it weak—which is why the best bridges and bones bend slightly!
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