tree (n.)

Old English treo, treow "tree" (also "timber, wood, beam, log, stake"), from Proto-Germanic *trewam (source also of Old Frisian tre, Old Saxon trio, Old Norse tre, Gothic triu "tree"), from PIE *drew-o-, suffixed variant form of root *deru- "be firm, solid, steadfast," with specialized senses "wood, tree" and derivatives referring to objects made of wood.

The line which divides trees from shrubs is largely arbitrary, and dependent upon habit rather than size, the tree having a single trunk usually unbranched for some distance above the ground, while a shrub has usually several stems from the same root and each without a proper trunk. [Century Dictionary]

The widespread use of words originally meaning "oak" in the sense "tree" probably reflects the importance of the oak to ancient Indo-Europeans. In Old English and Middle English also "thing made of wood," especially the cross of the Crucifixion and a gallows (such as Tyburn tree, famous gallows outside London). Middle English also had plural treen, adjective treen (Old English treowen "of a tree, wooden"). For Dutch boom, German Baum, the usual words for "tree," see beam (n.). Meaning "framework of a saddle" is from 1530s. Meaning "representation of familial relationships in the form of a tree" is from c. 1300. Tree-hugger, contemptuous for "environmentalist" is attested by 1989.

Minc'd Pyes do not grow upon every tree,
But search the Ovens for them, and there they be.
["Poor Robin," Almanack, 1669]

tree (v.)

"to chase up a tree," 1700, from tree (n.). Meaning "take a tree-like form" is from 1884. Related: Treed; treeing.

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Definitions of tree
tree (v.)
force a person or an animal into a position from which he cannot escape;
Synonyms: corner
tree (v.)
plant with trees;
this lot should be treed so that the house will be shaded in summer
tree (v.)
chase an animal up a tree;
her dog likes to tree squirrels
the hunters treed the bear with dogs and killed it
tree (v.)
stretch (a shoe) on a shoetree;
Synonyms: shoetree
tree (n.)
a tall perennial woody plant having a main trunk and branches forming a distinct elevated crown; includes both gymnosperms and angiosperms;
tree (n.)
a figure that branches from a single root;
genealogical tree
Synonyms: tree diagram
Tree (n.)
English actor and theatrical producer noted for his lavish productions of Shakespeare (1853-1917);
Synonyms: Sir Herbert Beerbohm Tree