Someone who crums; a person or thing characterized by producing crumbs or a crumbly condition.
From 'crum' plus the agent suffix '-ster' (as in 'trickster,' 'youngster'), which is an older way to create agent nouns; less common than '-er.'
The '-ster' suffix was hugely popular in Old and Middle English but became less common—we still see it in 'trickster,' 'youngster,' and 'gangster,' but '-er' took over as the default agent suffix.
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