"perennial plant growing from the ground with a self-supporting stem or trunk from which branches grow," Middle English tre, from 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.
Not found in High German except as the derived word for "tar." For Dutch boom, German Baum, the usual words for "tree," see beam (n.). Middle English also had plural treen, adjective treen (Old English treowen "of a tree, wooden").
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]
In early figurative use often of the trees in the Garden of Eden or the Tree of Life. In Old English and Middle English also mechanically, "thing made of pieces or frames of wood," especially the cross of the Crucifixion and later a gallows (such as Tyburn tree, the famous gallows outside London). The meaning "framework of a saddle" is from 1530s. A tree-nail (Middle English) was a wooden peg or pin used in ship-building.
The 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]
