One who or that which excites or stimulates; an agent of excitation.
From Latin 'excitator' (one who excites), derived from 'excitare' with the agent noun suffix '-tor/-tor.' This follows the same pattern as 'creator,' 'spectator,' etc.
The term 'excitator' appears more in older or specialized scientific writing; modern English prefers 'exciter.' But it's a beautiful example of how Latin word-building can create agent nouns for almost any verb.
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