at·a·rac·tic 
(ăt′ə-răktĭk) also at·a·rax·ic (-răksĭk)
(ăt′ə-răktĭk) also at·a·rax·ic (-răksĭk)adj.
Of or relating to a drug or other agent that has a tranquilizing effect.
[From Greek ataraktos, undisturbed : a-, not; see A-1 + taraktos, disturbed (from tarassein, tarak-, to disturb).]