相姦 is read as そうかん (soukan) and means adultery.
そうかん
soukan
そうかんこん
marriage following adultery and a subsequent divorce
きんしんそうかん
incest
ふしそうかん
paternal incest
すまい
sumo wrestling
そうさい
killing each other
あいずち
two smiths hammering at an object in turn
すまいとり
wrestler
あいて
opponent (sports, etc.)
そうば
market price
そうとう
considerable
そうだん
consultation
そうたいてき
relative