clog up

VERB
7 LETTERS · STARTS WITH C

clog up is a valid 7-letter word worth 11 points in Scrabble and 16 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
C3L1O1G2U1P3
3 + 1 + 1 + 2 + 0 + 1 + 3 =11 PTS
DOUBLE WORD → 22TRIPLE WORD → 33
MEANING

What does clog up mean?