Cosmic Origins Spectrograph 
Corporation for Open Systems 
central offices 
Class of Service 
Chief of Staff 
Coles 
Crystal Observation System 
Central Office Switch 
Compatible Operating System 
computer operating system 
Conservative Opportunity Society 
Console Operating System 
Cray Operating System 
Because 
Call Origination Status 
Camera Operating System 
Canadian Oncology Society 
Carry-on Oxygen System 
Cassette Operating System 
Change Of Subject 
Chief Of Station 
Clip On Socket 
Combat Operations Staff 
Commanding Officers 
Commercial Operating System 
Common Object Services 
Common Output Subsystem 
Communication OS 
Communications Segment 
Community of Science