Learn That Word

Synonyms for Agent (same or very similar meaning)

WordNet sense 1 (any agent or representative of a federal agency or bureau):
federal agent

WordNet sense 2 (a businessman who buys or sells for another in exchange for a commission):
broker, factor

WordNet sense 3 (the semantic role of the animate entity that instigates or causes the happening denoted by the verb in the clause):
agentive role

From the ODE community, based on WordNetadd/edit