Synonyms for White Alder (same or very similar meaning)
WordNet sense 1 (tree of western United States):
Alnus rhombifolia, mountain alderWordNet sense 2 (shrub of eastern and southern coastal United States having beautiful racemes of spice-scented white flowers):
sweet pepperbush, Clethra alnifolia, pepper bush, summer sweetFrom the ODE community, based on WordNetadd/edit