For definitions of terms as used contemporaneously, try early editions of Encyclopedia Americana or New International Encyclopaedia, both available at HathiTrust. See also the tab on "Law-Reference".
Index of All Reports Issued by Bureaus of Labor Statistics in the United States Prior to March 1, 1902.
Washington: GPO, 1902. There are entries on, for example, "convict [...]", "peonage", "prison [...]", "involuntary servitude", "contract [...]".
HathiTrust. Govt Docs La 1.2:In 2.