cod liver oil 
noun [mass noun]
Oil pressed from the liver of cod, which is rich in vitamins D and A.More than half of Irish adults use food supplements such as vitamins, minerals and cod liver oil, the organisation says....
- Use of other vitamin D supplements during the first year of life and maternal use of cod liver oil or other vitamin D supplements during pregnancy were not associated with type 1 diabetes.
- In 1941 the Vitamin Welfare Scheme was set up to issue cheap milk, concentrated orange juice, cod liver oil, and vitamin A and D tablets to pregnant women and children under 5.