1 To suppress a legal document, particularly a subpoena, for reasons based on defect in manner of service or for other procedural or substantive reasons that invalidate the document; to void or terminate; to vacate a judicial decision. 2 To suppress, as in quashing an uprising or revolt. quasi Latin. Alike in some sense, but not in actuality; resembling something but not really being it; nearly; almost like. quasi contracts.See contract. quasi criminal. A proceeding similar in nature to a cri...