Any of various instruments issued, esp. by corporations, as evidences of debt. Such instruments (often called debenture bonds) are generally, through not necessarily, under seal, and are usually secured by a mortgage or other charge upon property; they may be registered or unregistered. A debenture secured by a mortgage on specific property is called a mortgage debenture; one secured by a floating charge (which see), a floating debenture; one not secured by any charge a naked debenture. In general the term debenture in British usage designates any security issued by companies other than their shares, including, therefore, what are in the United States commonly called bonds. When used in the United States debenture generally designates an instrument secured by a floating charge junior to other charges secured by fixed mortgages, or, specif., one of a series of securities secured by a group of securities held in trust for the benefit of the debenture holders.