major tranquillizer

NOUN
19 LETTERS · STARTS WITH M

major tranquillizer is a valid 19-letter word worth 45 points in Scrabble and 52 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
M3A1J8O1R1T1R1A1N1Q10U1I1L1L1I1Z10E1R1
3 + 1 + 8 + 1 + 1 + 0 + 1 + 1 + 1 + 1 + 10 + 1 + 1 + 1 + 1 + 1 + 10 + 1 + 1 =45 PTS
DOUBLE WORD → 90TRIPLE WORD → 135
MEANING

What does major tranquillizer mean?