What does alder mean?
The definition of alder
Al”der, n.
Etym: [OE. aldir, aller, fr. AS. alr, aler, alor, akin to D. els, G. erle, Icel. erlir, erli, Swed. al, Dan. elle, el, L. alnus, and E. elm.] (Bot.)

A tree, usually growing in moist land, and belonging to the genus Alnus. The wood is used by turners, etc.; the bark by dyers and tanners. In the U. S. the species of alder are usually shrubs or small trees. Black alder. (a) A European shrub (Rhamnus frangula); Alder buckthorn. (b) An American species of holly (Ilex verticillata), bearing red berries.