Possibly taken from the plant family, Nerium oleander (flowering shrub known as oleanders), Cascabela thevetia (yellow oleander), Acacia neriifolia (oleander wattle); or a species of moth, Daphnis nerii (oleander hawk-moth).
In the complex language of love practiced during the time of Queen Victoria, the Oleander flower means caution.
A diminutive use of Oleander could be Ollie, Lee, Lee-Ann, or Anders.
In the English-speaking world this name has been occasionally given since the early 20th century. It started rising in America after the variant Lorelai was used for the main character (and her daughter, nicknamed Rory) on the television series Gilmore Girls (2000-2007).