Hair tonic is a popular hair product that is used to promote hair growth, strengthen hair roots and nourish the hair. It is also known as hair oil, hair revitalizer, and hair tonic. These synonyms all refer to the same product that is used to improve the health and appearance of hair. Hair oil is a lightweight liquid that is applied to the hair and scalp to hydrate and nourish the hair. Hair revitalizer is a term that suggests a product that will restore the health of damaged hair. Hair tonic is the most common term used to refer to hair products that promote hair growth and vitality.