Learn Finnish: Akrobaatti oli loistava. - The acrobat was brilliant.

You would ask Millainen akrobaatti oli? or Minkälainen akrobaatti oli?. Both of these words mean 'what kind of' or 'what like' and are used to ask about the qualities of something, perfectly prompting a descriptive answer like loistava.

Why is the adjective loistava in the nominative case instead of the partitive case (loistavaa)?

Because the subject, akrobaatti, is a singular, countable noun referring to a specific person. In Finnish sentences using the verb olla (to be), if the subject is a whole, indivisible person or thing, the describing adjective stays in the basic nominative case.

The word loistava ends in '-va'. Is it related to a verb?

Yes, it is formed from the verb loistaa (to shine). Adding the -va ending turns it into a present active participle, which acts like an English '-ing' word. Literally, the acrobat was 'shining', which is the standard way to say 'brilliant' or 'excellent' in Finnish.

How would this sentence change if there were multiple acrobats?

It would become Akrobaatit olivat loistavia. The subject takes the plural nominative ending (akrobaatit), the verb becomes the plural olivat, and the describing adjective must change to the plural partitive case (loistavia).