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.
Orange is also a surname, which may be derived from the medieval feminine name, or directly from the French place name. First used with the modern spelling in the 17th century, apparently due to William, Prince of Orange, who later became William III. His title is from the French place name.