Final answer:
The nickname for Snape given by the Marauders was 'Snivellus'.
Step-by-step explanation:
In the Harry Potter series, the Marauders, a group of Gryffindor students, had a brutal nickname for Severus Snape. They referred to him as 'Snivellus' due to his greasy and unattractive appearance. This derogatory nickname highlights the contentious relationship between Snape and the Marauders, particularly James Potter.