oo

noun2

1. •
   Any of four Hawaiian birds of the genus Moho, formerly classed with the honeyeaters and now believed to be extinct.

   • On this visit I made careful inquiries as to the success of Mr. Gay's efforts to raise the "Oo" bird on this island. — 1898
2. •
   (no longer used) (Ω, ω) The Greek letter omega.

   • Then came ther downe goodly ladyes tweyne […] And seyde, the gret Alpha & Oo most souereyne […] had hem thedyr sent. — 1500

adjective1

1. •
   Initialism of object-oriented.