↑ “Indogermanisches Etymologisches Wörterbuch”, J. Pokorny, 1959, Bern: Francke, pp. 911
Etymology
From shaj, ultimately from çaj, with -r doubling for expressive reasons. Compare Hittite šarra(“break, rupture, divide”), Latin serra(“id”), Lithuanian sėris(“filament”)[1]. Alternatively from Latin serra; compare Aromanian sharã.