Siwan merkilegu heiti: Örlátur, Virk, Kát, Vingjarnlegur, Skapandi. Fá Siwan merking nafns.
Siwan Uppruni fornafns. Welsh form of Joan. Fá Siwan Uppruni fornafns.
Samheiti fyrir Siwan í mismunandi löndum og tungumálum: Asia, Chevonne, Gia, Gianna, Giannina, Giovanna, Giovannetta, Hanna, Hanne, Hannele, Hannie, Ioana, Ioanna, Iohanna, Ivana, Jana, Jane, Janessa, Janice, Janina, Janna, Janne, Jannicke, Jannike, Jean, Jeanne, Jehanne, Jennigje, Jo, Joan, Joana, Joanie, Joaninha, Joann, Joanna, Joanne, Joasia, Joetta, Joey, Johana, Johanna, Johanne, Johanneke, Johnna, Jojo, Joleen, Jolene, Jone, Jonelle, Jonette, Joni, Jonie, Jonna, Jóhanna, Jóna, Jovana, Juana, Juanita, Nana, Seona, Seonag, Seònaid, Shauna, Shavonne, Shawna, Sheona, Shevaun, Shevon, Shona, Sìne, Síne, Siobhán, Tajuana, Vanna, Xoana, Yana, Yanka, Yanna, Yoana, Zhanna, Žana. Fá Siwan á öðrum tungumálum.
Algengustu nöfnin með eftirnafninu Neiswonger: Dreama, Garnet, Tristan, Giuseppe, Lorenza, Tristán. Fá Nöfn sem fara með Neiswonger.