Subtree

Part of speech: noun

Definitions

1. A portion of a hierarchical data structure consisting of one node together with all of the nodes beneath it
2. The set of nodes and connections descending from a single point in a branching structure such as a file system or parse tree
3. Any smaller tree formed by one node and everything underneath it, within a larger tree-shaped hierarchy

Etymology: A subtree is simply a tree that sits inside a larger one: any branch, together with everything growing from it, can be treated as a tree in its own right. The word is a plain compound of "sub-", from Latin "sub" meaning "under" or "below", and "tree", which English inherited from Old English "trēow" and which traces back through Proto-Germanic "trewą" to a much older root. Put together, the pieces describe exactly what the word means: a tree beneath or within another. The prefix does the work here. "Sub-" has been productive in English for centuries, so speakers could attach it to almost any noun to name a smaller part of the whole, as in "subsection" or "subcategory". The same logic carries over to computing and mathematics, where a subtree is a branch of a data structure that is itself a complete structure, which is why the term is common in programming. The word's history is therefore mostly the history of its two parts, both of which had long, separate lives before being joined.

Synonyms: branch, subbranch