I should have been clearer. A 'partial' on its own, would be a noun meaning a partial fingerprint. And I'm guessing an 'oblique' on its own would be a noun meaning an oblique fingerprint. Putting the two together, 'partial' becomes an adjective describing the 'oblique'.
In his sentence it was an adjective because he used it to modify the noun fingerprint.
When used on its own we could regard it as an adjective if we consider the word fingerprint to have been omitted through ellipsis. However, it can be used as a standalone noun too - these categorizations are not governed by any law and this type of duality is not uncommon.