Linden can also be spelled Lyndon, Lyndan, Lynden, Lindan, Lindon, and Lindyn.
Potential nicknames: Lin, Denny, Linzie, Linny, Lindy, Linda, Indy
Origin: German and English, meaning "linden tree," and commonly known as a "lime tree," although not the tree of the same name that produces limes. The spelling Lyndon, however, means "linden tree hill," and variants include Lyndale, Lyndall, and Lyndell.
Fun fact: President Lyndon B. Johnson.
Popularity: There were 57 baby boys named Linden in 2010 in the U.S., 5 boys named Lindan, 15 named Lindon, 37 Lyndon, and 106 Lyndon. Alternately, in 2010 as well, there were 54 baby girls named Linden, 36 named Lynden, 6 Lyndin, and 11 named Lyndon. I would say these statistics definitely make Linden a unisex name. In 2011 there were 120 boys named Lyndon, 66 Linden, 26 Lynden, 16 Lindon and 5 Lyndan. For girls, there were 51 named Linden in 2011, 14 Lindyn, 14 Lyndon and 22 Lynden.
"Here a linden tree stood, bright'ning
All adown its silver rind,
For as some trees draw the lightning,
So this tree, unto my mind,
Drew to earth the blessed sunshine
From the sky where it was shrined."
- Elizabeth Barrett Browning