"I read the chapter."
Translation:Ego lectionem lego.
Yes, you are right, Capitulum is a small caput. "ulum" is the diminutive form, like "et/ette" is the diminutive form in French and "ito/ita" is a diminutive form in Spanish.
It's called "caput" (head) for the same reasons a header is called a header in English. The mention "chapter" is placed at the top, as the head.
From the French lectionnaire, from the Latin lectionarium.
Lesson are from the French leçon. Root: lectio.
Lectio: selected text. (the first lessons were religious texts)
Lecture from the French lecture, meaning the action of reading, substantivation of the verb lire (to read). Late Latin lectura.
(I don't know if It had everything'correct).
Verb legere, means both to read, and to select (selected texts)
The meaning of selecting seems to have been lost in the modern Romance language (?), they kept only the "reading" meaning, (except maybe in "lessons"??)