1. undermargin - Noun
2. undermargin - Verb
The lower rim or margin of something.
The lower margin of a page or of an inset image on a page, where it is possible to add a caption.
(finance) A shortfall; the amount by which the value of an investment purchased on margin falls below the required maintenance amount.
(finance) To fall below margin; to create an undermargin.
To buy less on margin than one can afford.
Source: en.wiktionary.org