A person or thing that arouses, awakens, or stimulates someone to action or emotion.
From arouse plus -er (English agent suffix meaning 'one who does'). The -er ending creates an agent noun from the verb.
Your alarm clock is technically an 'arouser'—it's a device whose entire purpose is to interrupt sleep and wake you, making it one of the most universally disliked arousers of all time!
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