Provided with or having an assistant; supported by assistant workers.
From 'assistant' plus '-ed' (having or provided with). This suffix converts nouns into adjectives describing possession or accompaniment, as in 'bearded' or 'talented.'
This word is quite rare because English prefers different constructions—we'd usually say 'with an assistant' rather than 'assistanted,' showing how some theoretically possible words just never catch on because they feel awkward.
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