Related to Ancient Greek ξίφος (xíphos); either a loan, or from a common original source.
The same word is probably preserved in Egyptian zft, Coptic ⲥⲏϥⲉ (sēfe).
Dümichen (1867) suggested an Old Semitic saïf or sêf, Myres (1930) a possible Libyan or "Sea Peoples" word.
The root س ي ف (s y f) is denominal.
Compare Hebrew סַיִף (sáyif).