The antonym for the word "most unprolonged" is "prolonged." Prolonged means lasting for a long time or extended duration. It is the opposite of unprolonged, which means brief or short-lived. Some synonyms for prolonged are extended, drawn-out, and lengthy. Prolonged is often used to describe situations or events that go on for an extended period. For instance, a prolonged illness, a prolonged drought, a prolonged war, or a prolonged negotiation. Therefore, the antonym for most unprolonged, which is prolonged, indicates a state of being extended, continued, or prolonged.