short for open (adj.), early 13c. "not closed; not hidden;" originally as awake is from awaken, etc. As a verb, "to open," from mid-15c.; now obsolete or archaic. Middle English had ope-head "bare-headed" (c. 1300).
opafication
opal
opalescence
opalescent
opaque
ope
OPEC
op-ed
open
open-air
open-ended