relative aperture

17 LETTERS · STARTS WITH R

relative aperture is a valid 17-letter word worth 21 points in Scrabble and 25 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS

R1E1L1A1T1I1V4E1A1P3E1R1T1U1R1E1

1 + 1 + 1 + 1 + 1 + 1 + 4 + 1 + 0 + 1 + 3 + 1 + 1 + 1 + 1 + 1 + 1 =21 PTS

DOUBLE WORD → 42TRIPLE WORD → 63

MEANING

What does relative aperture mean?