linear unit

NOUN
11 LETTERS · STARTS WITH L

linear unit is a valid 11-letter word worth 10 points in Scrabble and 14 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
L1I1N1E1A1R1U1N1I1T1
1 + 1 + 1 + 1 + 1 + 1 + 0 + 1 + 1 + 1 + 1 =10 PTS
DOUBLE WORD → 20TRIPLE WORD → 30
MEANING

What does linear unit mean?