Because Oleander is a fairly known plant species, I think the mispronunciation may be too obvious and something you and your child will struggle with their whole lives. I believe it is “Oh-Lee-An-Der.” Not the best analogy, but it would be like naming them “Sunflower” and corrrecting everyone that their name is “Soon-flower.” However, that being said, I do like the name Oleander as it is and wonder if the correct pronunciation will grow on you. If you really don’t like it though, perhaps knowing while Oleander is a pretty flowering plant, it is very toxic when ingested, might make it easier for you to pursue other options. Not that you’d have to, but if it helps minimize any disappointment, it’s something to know. Was this name for a boy or girl? Perhaps, Berries could help you come up with additional flora/fauna type names with a similar vibe and originality. Congrats on your baby!