es·pal·ier. (ĭ-spăl′yər, -yā′) n. 1. A tree or shrub that is trained to grow in a flat plane against a wall or trellis, often in a symmetrical pattern. 2. A trellis or other framework on which an espalier is grown. tr.v. es·pal·iered, es·pal·ier·ing, es·pal·iers.