grudge / rancour
rancori
ran-KOH-reh
'Portare rancore' (to carry rancour) or 'covare rancore' (to harbour rancour) are the most common collocations.
Non portare rancore, cerca di perdonare.
Don't hold a grudge, try to forgive.
Il rancore avvelena chi lo prova.
Rancour poisons the one who feels it.