mid-13c., knouen, "well-known, famous, notorious," past-participle adjective from know (v.). From early 14c. as "recognized, not secret; familiar, not strange." As a noun, "that which is known," by 1863; earlier "famous person" (1835). In Middle English it meant "one's acquaintances." To make (something) known is from mid-14c.
a known quantity
a musician known throughout the world
the limits of the known world
a known criminal
know-how
knowing
know-it-all
knowledge
knowledgeable
known
know-nothing
knub
knuckle
knuckleball
knuckle-duster