peripheral

nouns

(computer science) electronic equipment connected by cable to the CPU of a computer
"disk drives and printers are important peripherals"

adjectives

on or near an edge or constituting an outer boundary; the outer area
"Russia's peripheral provinces"; "peripheral suburbs"
is derived from
antonym
is similar to
lying around or just outside the edges or outskirts
"circumferential highways around cities"
is similar to
at or constituting a border or edge
"the marginal strip of beach"
is similar to
being all around the edges; enclosing
"his encircling arms"; "the room's skirting board needs painting"
is similar to
located outside a military base
"off-base housing"
related to the key issue but not of central importance
"a peripheral interest"; "energy is far from a peripheral issue in the economy"; "peripheral issues"
is similar to
(sometimes followed by `to') minor or casual or subordinate in significance or nature or occurring as a chance concomitant or consequence
"incidental expenses"; "the road will bring other incidental advantages"; "extra duties incidental to the job"; "labor problems incidental to a rapid expansion"; "confusion incidental to a quick change"