Lily flower
An elaborated French-style spelling of Lillian, which itself is a derivative of Lily. It refers to the lily flower, which has long been a symbol of purity and innocence in Western culture.
Less common today
Lillianne isn't in the latest US Top 1000. It last peaked at #2,575 in 2013.
US births per 5-year period, 1990βpresent (SSA data).