The Collaborative International Dictionary of English v.0.48:

Oss \Oss\, v. i. [See Osse, n.]
   To prophesy; to presage. [R. & Obs.] --R. Edgeworth.
   [1913 Webster]

The Jargon File (version 4.4.7, 29 Dec 2003):

OSS


    Written-only acronym for “Open Source Software” (see open source). This
    is a rather ugly TLA, and the principals in the open-source movement
    don't use it, but it has (perhaps inevitably) spread through the trade
    press like kudzu.