In linguistics: the name of a case form expressing "into". Not just "in" (that's the inessive), not just "to" (that's the allative), but "into".

In Finnish the illative has the ending -n with the preceding short vowel lengthened: talo 'house', taloon 'into the house'. Long vowels and diphthongs keep an -h- between them and the vowel ending: maa ~ maahan.

It has a number of other idiomatic uses, e.g. starting an activity (kala 'fish', menen kalaan 'I'm going fishing').

The opposite case is the elative, for motion out of.