ataractic agent

NOUN
15 LETTERS · STARTS WITH A

ataractic agent is a valid 15-letter word worth 19 points in Scrabble and 23 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
A1T1A1R1A1C3T1I1C3A1G2E1N1T1
1 + 1 + 1 + 1 + 1 + 3 + 1 + 1 + 3 + 0 + 1 + 2 + 1 + 1 + 1 =19 PTS
DOUBLE WORD → 38TRIPLE WORD → 57
MEANING

What does ataractic agent mean?