Impetus and Synergist

Impetus noun - Something that arouses action or activity.

Synergist and impetus are semantically related In some cases you can use "Synergist" instead a noun "Impetus".

Synergist noun - A drug that augments the activity of another drug.

Impetus and synergist are semantically related in catalyst topic. You can use "Impetus" instead a noun "Synergist", if it concerns topics such as something which incites activity.