Synonyms for Freak (same or very similar meaning)
WordNet sense 1 (a person or animal that is markedly unusual or deformed):
monster, monstrosity, lusus naturaeWordNet sense 2 (someone who is so ardently devoted to something that it resembles an addiction):
addict, junkie, junky, nut, addictWordNet sense 3 (lose one's nerve):
freak out, gross outFrom the ODE community, based on WordNetadd/edit