arithmetic operation

NOUN
20 LETTERS · STARTS WITH A

arithmetic operation is a valid 20-letter word worth 28 points in Scrabble and 31 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
A1R1I1T1H4M3E1T1I1C3O1P3E1R1A1T1I1O1N1
1 + 1 + 1 + 1 + 4 + 3 + 1 + 1 + 1 + 3 + 0 + 1 + 3 + 1 + 1 + 1 + 1 + 1 + 1 + 1 =28 PTS
DOUBLE WORD → 56TRIPLE WORD → 84
MEANING

What does arithmetic operation mean?