/sa kahd", seuh-/ , n.
1. the act of checking a horse quickly with a single strong pull of the reins.
2. Ophthalm. the series of small, jerky movements of the eyes when changing focus from one point to another.
[ 1720-30; saccade jerk, jolt, orig., movement of a horseman who abruptly pulls the reins, equiv. to MF saqu ( er ) to pull violently (N dial. var. of OF sachier, ult. deriv. of sac SACK 1 , hence presumably with sense "withdraw from a sack") + -ade -ADE 1 ]