You use a. Use an only with words that start with a vowel sound.
A word that starts with s cannot start with a vowel sound, unless the s is actually pronounced like the name of the letter, which is not common. For example, you would say an S-hook, because that would be pronounced an ess-hook. However, for "normal" words that start with s, the article a is correct, as in a serious problem or a sock.
The word that is a synonym of "look hard" starting with S is "scrutinize."
One word that starts with "s" and ends with "n" is "salmon."
single, stairway, singer, safety, safely, secure, storage, spitting, sunny, someone, simple
It depends on how the "h" word is pronounced. Use "a" before words where the "h" is pronounced as a consonant sound (e.g., "a house"). Use "an" before words where the "h" is silent and the word is pronounced starting with a vowel sound (e.g., "an hour").
If the word you are making into a possessive ends in s because it is a plural, then you add an apostrophe after the s to make it possessive. In all other cases, including words which end in s for any reason other that because they are plurals, you add an apostrophe and the s.
The word that is a synonym of "look hard" starting with S is "scrutinize."
Seta is a 4-letter word for hair or bristle starting with S.
Stab -- an idiomatic use, as in, "He made a stab at getting the painting done."
what word starting with s is a synonym for technology? playful
Start
Santa
star
set
shelter
Steam
spotless
Sensational!