1. [adj]  so surprisingly impressive as to stun or overwhelm; "such an enormous response was astonishing"; "an astounding achievement"; "the amount of money required was staggering"; "suffered a staggering defeat"; "the figure inside the boucle dress was stupefying"
2. [adj]  walking unsteadily; "a stqaggering gait"

STAGGERING is a 10 letter word that starts with S.