noun

• (graph theory) A connected graph with no cycles or, if the graph is finite, equivalently a connected graph with n vertices and n−1 edges.
• (computing theory) A recursive data structure in which each node has zero or more nodes as children, but does not share children with other nodes.
• (graphical user interface) A display or listing of entries or elements such that there are primary and secondary entries shown, usually linked by drawn lines or by indenting to the right.
  "We’ll show it as a tree list."
• (often in the plural, slang) Marijuana.
  "I like good pussy and I like good trees / Smoke so much weed you wouldn't believe"

verb

• (transitive) To chase (an animal or person) up a tree.
  "The dog treed the cat."
• (transitive) To place in a tree.
  "Black bears can tree their cubs for protection, but grizzly bears cannot."
• (transitive) To place upon a shoe tree; to fit with a shoe tree; to stretch upon a shoe tree.
  "to tree a boot"
• (intransitive) To take refuge in a tree.

noun

• (mathematics) An extremely fast-growing function based on Kruskal's tree theorem.

noun

• (mathematics) Alternative letter-case form of TREE.