There are many words that can be used as synonyms for the phrase "lacking in magnanimity". Some of these include words such as petty, mean-spirited, small-minded, selfish, ungenerous, and stingy. These words all convey a sense of negativity and a lack of generosity towards others, which is the opposite of what it means to be magnanimous. It is important to choose the right words when describing someone's behavior or character, as subtle differences in language can greatly impact how others perceive them. Therefore, it is crucial to choose words that accurately convey one's sentiments without being overly harsh or judgmental.