sardonic

(sar-don’ik) [L. sard on’icus; Gr. Σαρδον- uxés Sard in i an]. Noting a kind of spasmodic or tetanic grin or involuntary smile, the ri’sus sard on’icus: so called from a plant of Sardinia, probably a Ranun’culus, or crowfoot, which was believed to produce it.