Is ill defined nodule in thyroid risky?

It depends: Thyroid nodules are common but most of them are benign. If you have shown it to your doctor, ask his/her advice for future monitoring. A sonogram(Ultrasound test) is one good way of following it and see if it grows in size. If it is clearly present and growing over 6 to 12 months, a needle biopsy should be considered. Your doctor can refer you to a Thyroid specialist(Endocrinologist) if you asked.