- any shrub or tree belonging to the genus Alnus, of the birch family, growing in moist places in northern temperate or colder regions and having toothed, simple leaves and flowers in catkins.
- any of various trees or shrubs resembling an alder.
- German chemist: Nobel Prize 1950.
- any N temperate betulaceous shrub or tree of the genus Alnus, having toothed leaves and conelike fruits. The bark is used in dyeing and tanning and the wood for bridges, etc because it resists underwater rot
- any of several similar trees or shrubs
