Something that forms, creates, or causes a crust to develop; or a person or thing that breaks up crusts.
From crust (Latin crusta) plus the agent suffix -er meaning 'one who does' or 'that which does.' It can mean either something that makes crusts or breaks them.
A 'cruster' in farming can refer to a tool that breaks up the crusty top layer of soil to help young plants push through—without breaking that crust, seedlings would waste all their energy fighting the hard ground.
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