semidarkness

NOUN
12 LETTERS · STARTS WITH S

semidarkness is a valid 12-letter word worth 19 points in Scrabble and 21 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
S1E1M3I1D2A1R1K5N1E1S1S1
1 + 1 + 3 + 1 + 2 + 1 + 1 + 5 + 1 + 1 + 1 + 1 =19 PTS
DOUBLE WORD → 38TRIPLE WORD → 57
MEANING

What does semidarkness mean?