Dictionary.net

A long strip of fine linen or cotton twist, passed through the skin and areolar membrane, to keep up an issue; or through suppurating cavities, between the fragments of fractured bones, &c., to fulfil certain indications. The term is, also, applied to the issue so established. The operation is simple. It consists in laying hold of a fold of skin, and passing a seton-needle through it, with the thread attached. Every day a fresh portion of the thread is drawn through the sore. Setons are established in many diseases; - in obstinate ophthalmia, cephalalgia; epilepsy, thoracic and abdominal affections, &c.; but they are not as much used as formerly.