Not wearing an apron; lacking an apron; without apron protection.
From 'apron' plus the suffix '-less' (without, lacking). This follows the standard English pattern of creating opposites with '-less,' as in 'helpless,' 'homeless,' or 'careless.'
An apronless cook would have been shocking in Victorian kitchens—it signaled either laziness or inexperience, since proper cooks always protected their clothing during food preparation!
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