(os) noun plural o·ra (ôr′ə, ō′rə) Anat.
A mouth or opening into the interior of an organ. [<L]

(os) noun plural os·sa (os′ə) Anat.
A bone, ob <L]

(ōs) noun plural o·sar (ō′sär) Geol.
A sinuous ridge of glacial sand and gravel, deposited by a stream flowing beneath; an esker: also spelled ose. [<Sw. ås a ridge, a chain of hills]

Chem.
Osmium (symbol Os).