Or, to quote from the episode:
Odo: "Well, as you know, when Dr. Mora first brought me to his laboratory, it was under Cardassian supervision. All specimen had to be clearly labelled in Cardassian, so the overseers would always know what the scientists were working on. Since no one was exactly sure what I was, Mora labelled me Unknown Sample, which the overseer translated into Cardassian as Odo'ital."
Fake Kira: "So, your name is Unknown Sample?"
Odo: "No, no. Odo'ital literally means the word 'nothing'. Even after it became clear that I was sentient, the Bajoran scientists kept calling me that. As a joke, they split it into two words like a Bajoran name, Odo Ital, which eventually got shortened."
The facts are unambiguous there, insofar as we can trust the juvenile Odo and his earliest memories. There are nuances there that warrant attention, though.
We don't learn from Odo's delivery whether the "joke" was cruel or intended as such - or just good-natured humor of the awkward sort that nerdy scientists so often practice.
It's quite possible the joke wouldn't be on Odo's expense as such, but directed more at the Cardassian oppressors and their hated language...
Timo Saloniemi
I agree. there is a good chance that the deep seated hatred every patriotic Bajoran had for the Cardassians in general would have expressed itself there.