debenture (n.) Look up debenture at Dictionary.com
"written acknowledgment of a debt," early 15c., from Latin debentur "there are due" (said to have been the first word in formal certificates of indebtedness), passive present third person plural of debere "to owe," originally, "keep something away from someone," from de- "away" (see de-) + habere "to have" (from PIE root *ghabh- "to give or receive").