What's the adjective for peripheries? Here's the word you're looking for.
Included below are past participle and present participle forms for the
verbs peripheralise and peripheralize which may be used as adjectives within certain contexts.
“A port is a slot on the computer where you can attach a peripheral device.”
“You know you're watching a bad zombie film when the zombies are peripheral to the suggestive outfits, time-and-space-defying stunts, and deliriously obnoxious soundtrack.”
“While every chapter makes reference to crucial historical markers, it offers a limited amount of names and dates that might be peripheral to the topic discussed.”