General:
* sûr(e) - sure, certain, safe
* sombre - gloomy, dark, somber
* soudain(e) - sudden, abrupt
* sage - wise, sensible, good
* sale - dirty, filthy
* singulier(ère) - singular, unique, strange
* simple - simple, easy
* sincère - sincere, genuine
* sombre - dark, gloomy
* sonore - resonant, sonorous
* sourd(e) - deaf, dull
* svelte - slender, slim
* strict(e) - strict, severe
Colors:
* sable - sand-colored
* sanguin(e) - blood-red
* saumon - salmon-colored
* sépia - sepia-toned
Descriptive:
* sec(he) - dry, arid, short
* séduisant(e) - seductive, charming
* serré(e) - tight, close
* silencieux(se) - silent, quiet
* sombre - dark, gloomy
* somptueux(se) - sumptuous, luxurious
* souple - flexible, supple
* sûr(e) - sure, certain, safe
Feelings:
* sain(e) - healthy, sound
* sauvage - wild, untamed
* sérieux(se) - serious, earnest
* sombre - gloomy, depressed
* souriant(e) - smiling, cheerful
* sûr(e) - sure, confident
This is just a small sample of the many French adjectives that start with "s." The list is not exhaustive.
Remember that French adjectives must agree in gender and number with the noun they modify.