There are over 700 words that match this clue. Here are some examples:
Sabbaticals
Sanitations
Snapdragons
Snowblowers
Specialists
Subdividers
Check the related links for a crossword solver tool, which is perfect for finding these sorts of words.
There are currently 2044 words that start with the letter "s" that have 12 letters total.
To find a list of all the words, please visit here: http://wordnavigator.com/by-length/12s/
Stop is a word of warning. It starts with the letter s. Shut up also can be a word of warning.
Sandman (starts with S ends with N - 7 letter word)
An eight letter word that starts with S and ends with T: satiristshortestsmallestsmarteststagnantstalwartstiffeststridentsubtract
Any 9-letter word that starts with s? Start with statetroom
im not sure about a 7 letter word, but i do know i 8 letter word that starts with s and means the right to vote, the word is... sufferage.
Socialization is a twelve letter word that begins with "s"
Showers describe precipitation. It begins with the letter s.
Shame
sincere
Semi
satisfying
sincere