Phonosemantic compound. 木 represents the meaning and 公 represents the sound. In simplified Chinese this character also means "relax, loosen", but in traditional Chinese this meaning is written as 鬆.
lax, loose; loosen, relax; loose; to loosen; to relax; floss (dry, fluffy food product made from shredded, seasoned meat or fish, used as a topping or filling)