What does dēscrīptor mean in Latin?

dēscrīptor, a noun, means “descriptor (that which describes)”.

What is the genitive of dēscrīptor?

The genitive singular is dēscrīptōris. dēscrīptor is masculine, third declension.

In classical Latin, [deːˈskriːp.tɔr]; in ecclesiastical (church) Latin, [deˈskrip.tor].

noun · masculinethird declension

dēscrīptor m (genitive dēscrīptōris, feminine dēscrīptrīx)

Classical[deːˈskriːp.tɔr]Ecclesiastical[deˈskrip.tor]

Late Latindescriptor (that which describes)
mōrum vitiōrumque pūblicōrum et dēscrīptor vērissimusand a most faithful descriptor of public morals and vices303 CE – 311 CE, Lactantius, Institutiones Divinae 5.9.19
dēscrīptōribus gentiumfor the descriptors of nations [i.e. the ethnographers]380 CE – 392 CE, Ammianus Marcellinus, Res Gestae 23.6.1

dēscriptor, ōris, m. describo,

I. a describer, delineator: morum, Lact. 5, 9, 19: descriptores gentium, ethnographers, Amm. 23, 6, 1.

From dēscrīptum + -tor.