defame; slander; ruin someone's reputation
My enemies have started these ugly rumors to denigrate me.
de (completely)#niger nigris (black) (Latin)
belittle, denigrate, deride, disdain, disparage, revile, vilify
Read denigrate as degrade, which means to defame or put a black blot on someone. DENIGRATE=DENY+GREAT. So if you deny someone is great, it means you BELITTLE him.