वचनाद्वा माधवः ।मधुनामानमसुरं सूदितवानिति मधुसूदनः ।
In plain words
Or else, on the strength of that scriptural line, he is Mādhava. He struck down the demon named Madhu — and that is why he is Madhusūdana.
Close to the Sanskrit
Or, from the [scriptural] statement, [He is] Mādhava. "He destroyed the demon whose name was Madhu" — thus, Madhusūdana.