Yes, es is a Scrabble word!
...and is worth 2 points in Scrabble, and 2 points in Words with Friends
es
Noun
1. A radioactive transuranic element produced by bombarding plutonium with neutrons
2. A fat-soluble vitamin that is essential for normal reproduction; an important antioxidant that neutralizes free radicals in the body
3. A radioactive transuranic element produced by bombarding plutonium with neutrons
4. The cardinal compass point that is at 90 degrees
5. The base of the natural system of logarithms; approximately equal to 2.718282...
6. The 5th letter of the Roman alphabet