To Deny
する verb
If 否定 is "denial," then the verb version would be to deny.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own. Will help to know the word 否定 as well.
私は納豆がご飯に合うって説は否定しますね。
I deny the theory that natto goes well with rice.