Merriam-Webster Collegiate Dictionary - alder

 biographical name Kurt 1902-1958 German chemist ALDER  noun  Etymology: Middle English, from Old English alor; akin to Old High German elira ~, Latin alnus  Date: before 12th century any of a genus (Alnus) of toothed-leaved trees or shrubs of the birch family that have catkins which become woody, that typically grow in cool moist ground, and that have wood used especially in turnery; also its wood