(C)omputer (O)utput on (M)icrofilm

from Latin com-; related to cum with. In compound words of Latin origin, com- becomes col- and cor- before l and r, co- before gn, h, and most vowels, and con- before consonants other than b, p, and m. Although its sense in compounds of Latin derivation is often obscured, it means:together, with, etc (combine, compile); similar (conform); extremely, completely (consecrate)