Questions & Answers about Kupissa on vielä teetä.
Why is "tea" written as teetä instead of just tee?
Because "tea" is an uncountable substance (a mass noun). When you say there is "some" of a substance in a place, Finnish uses the partitive case. Here, it means there is an unspecified amount of tea in the cup.
Why does teetä get the -tä ending instead of just -ä?
The base word is tee. When a Finnish word ends in two vowels, the partitive ending is usually -ta or -tä. Since tee only contains the front vowel "e", vowel harmony rules dictate we use the front-vowel ending -tä.
Why doesn't the sentence use a word for "there", like in the English translation?
The dictionary word for cup is kuppi. Why does kupissa only have one "p"?
Adding the -ssa ("in") ending triggers a rule called consonant gradation. Because the ending closes the final syllable, the strong double pp weakens into a single p.