The epithet Nīlakaṇtha (Sanskrit नीलकण्ठ; nīla = "blue", kaṇtha = "throat"). Since Shiva drank the Halahala poison churned up from the Samudra Manthan to eliminate its destructive capacity. Shocked by his act, Goddess Parvati strangled his neck and hence managed to stop it in his neck itself and prevent it from spreading all over the universe, supposed to be in Shiva's stomach. However the poison was so potent that it changed the color of his neck to blue.
The Sanskrit word Shiva comes from Shri Rudram Chamakam of Taittiriya Samhita of Krishna Yajurveda. The root word śi means auspicious. In simple English transliteration it is written either as Shiva or Siva. The adjective śiva, is used as an attributive epithet not particularly of Rudra, but of several other Vedic deities. ....... Title has been given since some of these facts may be shocking for someone, soothing for devotees and interesting for others. Some of these facts may be known to someone but unknown to other.