ETYM Old Eng. aldir, aller, from AS. alr, aler, alor, akin to Dutch els, German erle, Icel. erlir, erli, Swed. al, Dan. elle, el, Latin alnus, and Eng. elm.
Any tree or shrub of the genus Alnus, in the birch family Betulaceae, found mainly in cooler parts of the northern hemisphere and characterized by toothed leaves and catkins.
Sitka alder A. sinuata and red alder A. rubra are common to W North America.
1. North temperate shrubs or trees having toothed leaves and conelike fruit; bark is used in tanning and dyeing and the rot-resistant wood; SYN. alder tree.
2. Wood of any of various alder trees; resistant to underwater rot; used for bridges etc.