A scientist was someone who studied or practised sciences.
Scientist was one of the Sensorites' ranks on the Sense Sphere, and was denoted by a swirling pattern insignia worn on the chest of the scientists' grey bodysuits. Two Sensorite scientists treated John, the mineralogist on Captain Maitland's ship, to restore his mind after he was driven insane. (TV: The Sensorites)
Soldeed was the last surviving scientist and de facto leader of the planet Skonnos. He arranged a deal with the Nimon so Skonnos could conquer the galaxy. When he discovered the Nimon would not honour their agreement, he could not believe it. He was killed by Seth. (TV: The Horns of Nimon)