Perhaps today the meanings are different (one is a superset). But according to Von Mises:

"In the terminology of Marx and Engels the words communism and socialism are synonymous. They are alternately applied without any distinction between them. The same was true for the practice of all Marxian groups and sects until 1917. "

http://oll.libertyfund.org/titles/1060#lf0069_label_908

Also, uses of "Liberalism" has been changed even more throughout the history.