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"Pickasliffer" does not have a standard definition in English language. It may be a made-up word or slang term with no commonly understood meaning.
This is an assignment from Daily Dazzle week 2. You decide what a dundifier is and what their job is. The same goes for a "pickasliffer". I suggest taking the word apart and finding out what each part means, for example if you google search "sliffer" you get pictures of dragons! Use this to help you think of what these might mean!