stoic
start
Bellybuttons would be the longest word I can think of beginning with a 'b' and ending in an 's'.
knapsacks
slippers, scissors
Syrah
swimmingly
No 7 letter words, but using 6 letters, words beginning with c, ending in s, are clouts and cutlets.
"Imperils" is a word that fits these qualifications.
Sasquatch, sixteenth, squeamish
Sasquatch, sixteenth, squeamish
storage