Learn Finnish: Odotan täällä viisi päivää.

In Finnish, any number greater than 1 requires the noun that follows it to be in the partitive singular form. Since viisi (five) is more than 1, the basic word päivä (day) takes the partitive ending -ä to become päivää.

The dictionary form for to wait is odottaa. Why does odotan only have one t?

This happens because of a spelling pattern called consonant gradation. When you add the -n ending to say I wait, the last syllable becomes closed because it ends in a consonant instead of a vowel. This change forces the strong double tt in odottaa to soften into a weak single t in odotan.

I learned that odottaa forces the word after it to be partitive. Is that why päivää is partitive?

Good catch, but not in this case! It is true that if you wait for a person or thing, that target must be partitive, as in Odotan bussia (I wait for the bus). However, viisi päivää tells us how long you wait, not what you are waiting for. The word päivää is partitive strictly because it comes directly after the number viisi.

Why use täällä instead of tässä for here?