What does ātrāmentārium mean in Latin?

ātrāmentārium, a noun, means “inkstand, inkhorn”.

What is the genitive of ātrāmentārium?

The genitive singular is ātrāmentāriī. ātrāmentārium is neuter, second declension.

noun · neutersecond declension

ātrāmentārium n (genitive ātrāmentāriī or ātrāmentārī)

ātrāmentārĭum, ii, n. atramentum,

I. an inkstand: atramentarium scriptoris, Vulg. Ezech. 9, 2 (as transl. of the Heb. ); 9, 3; 9, 11.

From ātrāmentum (“ink”) + -ārium (“place for”).