Definition of ob:
part of speech: noun
A prefix meaning " in the way of"; " against," as in obviate; ob becomes oc before c, as in occasion: of before f, as in offend; o before m, as in omit; and op before p, as in oppose; in bot., ob means " reversed"- thus: " cordate" means heart- shaped, with the attachment at the broad end; " obcordate" means heart- shaped, but with the attachment at the narrow end.
Dat comes ob bein' civilized.W. Clark Russell in "The Frozen Pirate".