Old woods, naturalcy enhancer, peppery, earthy.
The quality of this one really matters, because the naff ones smell more of cheap alpha terpineol, rather ruining the beautiful foresty fencepost realism of true terpineol-4.
Having rejected a few lower grades of the years I think I've finally found the best; in this case made by a flavour company primarily for flavourists and hence ruthlessly rejectionary about stray impurities.