A small anatomical band, fold, or ligament that restrains or limits the movement of a body part, such as the tissue under the tongue.
From Latin fraenulum, diminutive of fraenum (bridle, restraint). Used directly in medical/anatomical Latin for centuries.
The fraenulum under your tongue is why some people are 'tongue-tied'—if it's too short, it restricts your tongue's range of motion, literally proving that Latin anatomy words describe real, physical limits.
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