aspen n.

suffix added to nouns to produce adjectives meaning "made of, of the nature of" (such as golden, oaken, woolen), corresponding to Latin -anus, -inus, Greek -inos; from Proto-Germanic *-ina- (from PIE *-no-, adjectival suffix).

Common in Old, Middle, and early Modern English: e.g. fyren "on fire; made of fire," rosen "made or consisting of roses," hunden "of dogs, canine," beanen "of beans," baken "baked," breaden "of bread;" Wycliffe has reeden made of or consisting of reeds." The few surviving instances are largely discarded in everyday use, and the simple form of the noun doubles as adjective (gold ring, wool sweater). Some are used in special contexts (brazen, wooden).

"lime tree," 1570s, noun use of an adjective, "of linden wood," from Old English lind "linden" (n.), from Proto-Germanic *lindjo (source also of Old Saxon linda, Old Norse lind, Old High German linta, German linde), probably from PIE *lent-o- "flexible" (see lithe); with reference to the tree's pliant bast. Compare Russian lutĭijó "forest of lime trees," Polish łęt "switch, twig," Lithuanian lenta "board, plank."

For modern tree names from adjectives, compare aspen. OED suggests the use of the adjective as a noun is at least partly creditable to "translations of a German romance" (German linden is the plural form and the form used in compounds).