Yes, king is a Scrabble word!

Noun

1. A male sovereign; ruler of a kingdom

2. A competitor who holds a preeminent position

3. A very wealthy or powerful businessman

4. Preeminence in a particular category or group or field

5. United States woman tennis player (born in 1943)

6. United States guitar player and singer of the blues (born in 1925)

7. United States charismatic civil rights leader and Baptist minister who campaigned against the segregation of Blacks (1929-1968)

8. A checker that has been moved to the opponent's first row where it is promoted to a piece that is free to move either forward or backward

9. One of the four playing cards in a deck bearing the picture of a king

10. (chess) the weakest but the most important piece