major tranquilliser

NOUN
19 LETTERS · STARTS WITH M

major tranquilliser is a valid 19-letter word worth 36 points in Scrabble and 43 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
M3A1J8O1R1T1R1A1N1Q10U1I1L1L1I1S1E1R1
3 + 1 + 8 + 1 + 1 + 0 + 1 + 1 + 1 + 1 + 10 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 =36 PTS
DOUBLE WORD → 72TRIPLE WORD → 108
MEANING

What does major tranquilliser mean?