Definition of tree

1 a : a woody perennial plant having a single usually elongate main stem generally with few or no branches on its lower part

b : a shrub or herb of arborescent form

• rose trees

• a banana tree

2 : something in the form of or resembling a tree: such as

a : a diagram or graph that branches usually from a simple stem or vertex without forming loops or polygons

• a genealogical tree

• phylogenetic trees

b : a much-branched system of channels especially in an animal body

• the vascular tree

3 a (1) : a piece of wood (such as a post or pole) usually adapted to a particular use or forming part of a structure or implement

(2) archaic : the cross on which Jesus was crucified

b archaic