- (of interest) payable on both capital and the accumulated interest:compound interestCompare with simple.
late Middle English compoune (verb), from Old French compoun-, present tense stem of compondre, from Latin componere 'put together'. The final -d was added in the 16th century on the pattern of expound and propound
The sense of the verb compound that means ‘worsen,’ as in this compounds their problems, has an interesting history. It arose through a misinterpretation of the phrase compound a felony, which, strictly speaking, means ‘forbear from prosecuting a felony in exchange for money or other consideration.’ The ‘incorrect’ sense has become the usual one in legal uses and, by extension, in general senses too, and is now accepted as part of standard English.