upon one's guard

ADJECTIVE
16 LETTERS · STARTS WITH U

upon one's guard is a valid 16-letter word worth 17 points in Scrabble and 23 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
U1P3O1N1O1N1E1'0S1G2U1A1R1D2
1 + 3 + 1 + 1 + 0 + 1 + 1 + 1 + 0 + 1 + 0 + 2 + 1 + 1 + 1 + 2 =17 PTS
DOUBLE WORD → 34TRIPLE WORD → 51
MEANING

What does upon one's guard mean?

ADJECTIVE · 1 SENSE