In a manner not favorable to success or to interest, profit, or reputation; with loss or inconvenience.

adverb. In a disadvantageous manner.

adverb. in a disadvantageous way; to someone's disadvantage

"His partiality to the smoking room leads him to be rather unfair to the liner's other large gathering space, the Grand Salon, illustrated disadvantageously in the book with shots that do not convey either its elegance or its comfort."

advantageously