In linguistics, a case used to indicate that one thing has been translated or transformed into another. I have only seen examples in Finnish, though related Finno-Ugrian languages also use it.

In Finnish the ending is -ksi. Examples of physical change are Talo paloi tuhaksi 'The house burned to ashes' and Lumi muuttui vedeksi 'The snow turned to water'.

Mental translation occurs in Sanokaa tämä suomeksi 'Say this in Finnish' (suome-, stem of Suomi 'Finland'), and with verbs like 'name', 'think': hyvä poika 'good boy' --> Kutsuin häntä hyväksi pojaksi 'I called him a good boy'.

It is also used for purpose: miksi? 'why?', Sain kirjan lahjaksi 'I got the book as a present'. There are other idiomatic uses.

The ending is actually -kse-, but final -e becomes -i in Finnish. The original vowel is restored when another suffix is added: Terveydeksenne! = 'to your health!' (-nne = 'your').

When added to the infinitive of a verb (the so-called Infinitive I, to be precise) it indicates purpose, and always has a personal ending: oppia 'to learn', Luette oppiaksenne 'You are reading in order to learn', Poika lukee oppiaksensa 'The boy is reading in order to learn' (-nsa 'his/her').