The word you're looking for is opaque.
Origin
optimism
One weather word that starts with an O is "overcast," which describes a sky that is completely covered by clouds.
ozone
The Maori word for talk starting with a "k" and ending with an "o" is "kΕrero."
Summer = KAH-yeets (קיץ) winter = KHO-ref (חורף) summer or winter = o kah-yeets o kho-ref (או קיץ או חורף)
observantold-fashionedoutgoing
origin.
Offers?
opportunistic
obi