Incentive and Synergist

Incentive noun - Something that arouses action or activity.

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

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

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