1570s, from medical Latin diastole, from Greek diastole "drawing asunder, dilation," from diastellein, from dia- "through, thoroughly, entirely" (see dia-) + stellein "to set in order, arrange, array, equip, make ready," from PIE *stel-yo-, suffixed form of root *stel- "to put, stand," with derivatives referring to a standing object or place (see stall, n.1).