Good base definition to start with (dictionary.com):
noun noun: scapegoat; plural noun: scapegoats
1. a person who is blamed for the wrongdoings, mistakes, or faults of others, especially for reasons of expediency. Similar: whipping boy victim Aunt Sally goat fall guy patsy
2. (in the Bible) a goat sent into the wilderness after the Jewish chief priest had symbolically laid the sins of the people upon it (Lev. 16).
verb verb: scapegoat; 3rd person present: scapegoats; past tense: scapegoated; past participle: scapegoated; gerund or present participle: scapegoating
make a scapegoat of. "few things are harder for kids to bear than being scapegoated"
Origin mid 16th century: from archaic scape ‘escape’ + goat.