This one really threw me for a loop. When I first smelled Black Pepper (Piper nigrum), it smelled like celery to me. Light, green/unripe, and tangy. When I looked to see what it was, I was stunned that it was Black Pepper. I think this is because the previous times I smelled and used Black Pepper, I assumed it would smell like the black pepper spice we use for cooking. My mind projected the smell of ground peppercorn onto this essential oil, because when I smell it - really smell without knowing what it is, and thus without any preconceived notions - I smell something lighter and greener. After an hour or so, it definitely smelled peppery.
Like ground peppercorn, Black Pepper essential oil comes from the unripe fruit/berry of the flowering vine. Unripe fruits are picked off, dried, and for essential oil, extracted through steam distillation. Black Pepper essential oil, however, does not contain piperene, the constituent which makes you sneeze and irritates the mucous membrane, which I think may give ground peppercorn that strong peppery aroma which I don't find as much with the essential oil.
I classify this as: light, green and peppery.