As FB says, clearic I think is the word you are after.
As to why it tastes smoother than CS aged spirit - not sure, but my guess would be that clearic is simply pure spirit (or in chemical terms simply ethanol) but after maturing in wood it will pick up more flavour compounds and congeners (fatty acids) from the tannins and vanillins in the wood, therefore it will taste more complex and as such more mouthfeel or burn. Hope that makes sense!
Is'nt it amazing what you can remember from Higher Chemistry! I remember once we made alcohol by fermenting orange juice, it tasted foul but as we were all 14 year olds we sure gulped it down.