tree related to the birch, Old English alor "alder" (with intrusive -d- added 14c.; the historical form aller survived until 18c. in literary English and persists in dialects, e.g. Lancashire owler, which is partly from Norse), from Proto-Germanic *aliso (cf. Old Norse ölr, Danish elle, Swedish al, Dutch els, German erle), from *el-, the ancient PIE name of the tree (cf. Russian olicha, Polish olcha, Latin alnus, Lithuanian alksnis).
Alder Al·der (äl'dər), Kurt. 1902-1958.
German chemist. He shared a 1950 Nobel Prize for discoveries concerning the structure of organic matter.