1cm neck lymph node for 4 months. ultrasound of node was normal. does this rule out malignancy, since 4 months no growth and normal ultrasound?

Yes: For the most part yes. Typically nodes will swell after and viral process. Sometimes the node does not shrink. I have had a similar node for years. If the character of the node would get spongy this is more concerning. Keep an eye on things, but I would have low suspicion for cancer.

Node: It does sound simple and not malignant. However the only way to have a definitive pathology is biopsy which is not indicated. Good Luck