To move about in a disorganized or agitated manner; to fuss and bustle about without accomplishing much.
Possibly related to 'fuss' with an altered form, or from 'fustian' (bombastic speech), suggesting agitated, ineffective movement or speech.
Some words capture behaviors that feel very real but don't make logical sense linguistically—'fuster' is one of those wonderfully onomatopoetic words that sound like what they describe.
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