Steam
soot
Another word for opportunity which begins with 'S' is scope.
bias
One word would be "prince". Add an -s and you have the plural - "princes". Add another -s and you have "princess", a word in singular form.
softening
shelter
Sensational!
scoundrel
Supervisor
screwdriver
Irks
* short, slight
Sharp or spirited.
skein
stupendous
sports
despises