The word "styleless" refers to the lack of any distinct or recognizable style. Luckily, the English language offers several synonyms for this adjective, including plain, ordinary, unadorned, unembellished, and devoid of panache. Other suitable substitutes for "styleless" include basic, drab, dull, uninteresting, uninspired, and unimaginative. If you're looking for more expressive terms, try using phrases such as characterless, featureless, personality-free, or lacking flair. Whatever words you choose to use, they should convey the idea that something is unremarkable or unremarked on, without any discernable or distinctive qualities.