verb

• (transitive) To unite by interweaving, as (horticulture) branches of shrubs, trees, etc., to create a hedge; to interlock, to plash.
  "Her Vine, the merry chearer of the heart, / Vnpruned, dyes: her Hedges euen pleach'd, / Like Priſoners wildly ouer-growne with hayre, / Put forth diſorder'd Twigs: [...]"

noun

• (horticulture) A branch of a shrub, tree, etc., used for pleaching; a pleacher.
  "These stems should be stripped (or nearly so) of their branches, and notched at the bottom (in the way which every hedger knows) to form a pleach: these pleaches should be laid in the intervals along the line of the stubs, and again notched, [...]"
• (horticulture) A notch cut into a branch so that it can be bent when pleaching is carried out.
  "Traditional hedge laying involves, first, clearing away undergrowth and weeds, particularly from a hedge that has been neglected and allowed to grow tall. Untidy side branches are removed. A cut, known as a pleach, is made in the back of the trunk, leaving a 'hinge'; old-time hedgers recommend that this should be as thick as a lamb's tongue."