sidereal second

15 LETTERS · STARTS WITH S

sidereal second is a valid 15-letter word worth 18 points in Scrabble and 21 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS

S1I1D2E1R1E1A1L1S1E1C3O1N1D2

1 + 1 + 2 + 1 + 1 + 1 + 1 + 1 + 0 + 1 + 1 + 3 + 1 + 1 + 2 =18 PTS

DOUBLE WORD → 36TRIPLE WORD → 54

MEANING

What does sidereal second mean?