Synthetic essential oils are sometimes called "fragrance oils", or just fragrances. They are often composed of up to 95% petroleum-derived chemicals. Among the some 3000 chemicals used, according to the EPA they often include acetone; benzaldehyde; benzyl acetate; benzyl alcohol; ethyl acetate; limonene; and methylene chloride. Up until about 40 years ago, most perfumes were made with essential oils. But now they are almost all synthetic. Synthetic fragrances are used in candles, soaps, kitchen cleaners, etc, etc. In 2002 a study of common scented beauty products (deodorants, perfumes, nail polish, hair spray) showed that 75% of them contained phthalates, industrial chemicals linked to birth defects.
The fragrance industry is self-regulated, like the art materials industry - that's why you can still buy lead white. When the term "fragrance" is used, a manufacturer is not required to disclose the ingredients. Legally, it is considered "proprietary", and can have pretty much anything in it. The same for the art industry. Very few artist paint manufacturers will tell you all of what is in their paint. There are ingredients that are simply not disclosed, and this is common industry practice.
So ---- in the case of synthetic spike oil, they can call it a fragrance and we will never know what’s really in it, but it would be a very different substance than what we now call Oil of Spike Lavender.