footnote-n; 2 Senses

Sense Number 1: explanatory notes/commentary in a document

Commentary: FOOTNOTE[+entity][+artifact][+document][+supplement][+commentary][+explanatory]

The footnotes for each chapter are listed at the end of the chapter.
There is a brief description of that poem in footnote 4 of chapter two.
The footnotes of the book are printed in a smaller font than the main text.

WordNet 3.0 Sense Numbers: 1

Sense Number 2: a subordinate part of an event, work or field

Commentary: FOOTNOTE[+relation][+role][+subordinate][+work/+event/+field]
NOTE: a somewhat figurative extension of Sense 1

It has been said that all of western philosophy is but a footnote to Plato.
That battle was only a footnote in the context of the 100-year War.
It's a movement now regarded as just a footnote to modern architectural trends.

WordNet 0.0 Sense Numbers: 2a