The Collaborative International Dictionary of English v.0.48:

Oo \Oo\, a.
   One. [Obs.] --Chaucer.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

oo \o"o\, n. [Hawaiian.] (Zool.)
   Any of several beautiful birds of the genus Moho, including
   the extinct Moho nobilis. They are honey-eaters native to
   the Hawaiian Islands. It yields the brilliant yellow feathers
   formerly used in making the royal robes. Called also
   yellow-tufted honeysucker.
   [1913 Webster]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

OO
       Object Orientated


The Free On-line Dictionary of Computing (30 December 2018):

object-oriented
object-orientation
OO

   1.  (OO) Based on objects, classes and methods,
   as in object-oriented programming or object-oriented design.
   An object-oriented database applies the same concepts to the
   storage of objects.

   2.  vector graphics.

   (2014-01-06)