The word dulia comes from the Greek doulia (meaning "slavery" or "servitude"). But in Catholicism, the word has taken on a theological meaning, as described in the Catholic Encyclopedia, "signifying the honour paid to the saints."
I see the connection between servitude and veneration, in that a servant shows a sort of respect to his master. But yet the two meanings, I think, are distinct enough that this transition wouldn't have been automatic.
So, I'd like to know when this transition occurred. Did the "veneration" meaning first appear in Latin, or originally in Ancient Greek? I know from that CE entry that Augustine weighed in on this subject, so it seems to have happened at least that early, but did it happen earlier than that?