escapement error

16 LETTERS · STARTS WITH E

escapement error is a valid 16-letter word worth 21 points in Scrabble and 25 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS

E1S1C3A1P3E1M3E1N1T1E1R1R1O1R1

1 + 1 + 3 + 1 + 3 + 1 + 3 + 1 + 1 + 1 + 0 + 1 + 1 + 1 + 1 + 1 =21 PTS

DOUBLE WORD → 42TRIPLE WORD → 63

MEANING

What does escapement error mean?