Semi
A 13-letter word that starts with "s" and ends with "s" is "schoolteachers."
An eight letter word that starts with S and ends with T: satiristshortestsmallestsmarteststagnantstalwartstiffeststridentsubtract
Sandman (starts with S ends with N - 7 letter word)
Scissors is an 8 letter word. It begins and ends with S.
Senselessness
aunts
Santana
Suffragettes.
stomata
Strains
darts
nabutas