Hi, Tiiu is a fairly common estonian name. Here in Finland, the local variant is Tiia. Tiiu is used here, too, but it's much rarer. In Finland, Tiiu is almost always used as an affectionate nickname for Tiia. Both names are of the same root as Tia - origins most likely in Spanish/Italian. It is a clipping of a longer name such as Dorothea that end in -thea (Thea -> Thia -> Tia ->Tiia -> Tiiu). And Thea is Greek for "god". I hope this helps!