mull over

VERB /məl_'oʊvər/
9 LETTERS · STARTS WITH M

mull over is a valid 9-letter word worth 13 points in Scrabble and 18 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
M3U1L1L1O1V4E1R1
3 + 1 + 1 + 1 + 0 + 1 + 4 + 1 + 1 =13 PTS
DOUBLE WORD → 26TRIPLE WORD → 39
MEANING

What does mull over mean?