compendium

From Latin compendium, meaning "that which is weighed together" or "a saving, an abbreviation," built from com- ("with") plus pendō ("to weigh").

The word began as a literal image of things weighed together, which gave it the sense of something shortened or economized — a saving of time or effort — before it settled into naming a condensed collection of knowledge.

It shares its root pendō, "to weigh," with the idea of weighing things jointly — the same weighing sense that gives compendium its core meaning of condensing or saving.