Learn German: Meine Tante ist geschieden.

In German, adjectives and past participles used as adjectives only take endings when they come directly before the noun they describe (like meine geschiedene Tante). When they come after a verb like ist (is), they are called predicate adjectives and keep their basic, uninflected form.

Is geschieden a verb or an adjective in this sentence?

It acts as an adjective here, describing her current status. It is built from the past participle of the verb scheiden (to separate or divorce). Using a form of sein (to be) plus a past participle is a common way to describe a resulting state or condition in German.

If I want to say 'My aunt got divorced,' can I just say Meine Tante war geschieden?

Not quite! Meine Tante war geschieden means 'My aunt was divorced' (referring to her status in the past). If you want to talk about the actual event or action of getting divorced, German usually uses the reflexive phrase sich scheiden lassen. So, 'My aunt got divorced' would be Meine Tante hat sich scheiden lassen.