essential oil 
noun
A natural oil typically obtained by distillation and having the characteristic odour of the plant or other source from which it is extracted.Sometimes, the hot steam or water used to distill an essential oil does not extract much natural oil from the plant or harms the precious natural oil....
- Quality essential oils are an important part of any aromatherapy programme.
- Combine basil essential oil with other essential oils to make perfumes and toilet water.