Added 9 October 2026 sium noun Categories: PlantsObscure Words noun ! Definition from WordNet 3.1, Princeton University. More about sium at Wordnik → Where our words come from → Perennial of wet and marshy places in the northern hemisphere: water parsnips. Related Words: maalinabunaalulaabdalsaimirabbesirakiadenifirdausiminahatat Back to today's word