Other forms: lanker; lankly; lankest
Lank can describe grass that is long, hair that is limp, and people who are tall and thin.
From the Old English hlanc (which is fun to say out loud), meaning loose and empty, lank is an adjective used to describe plant life which is long and slender, hair that hangs long and limp, and people who are long and slim. So you might hire a lank basketball player with lank hair to cut the grass when it’s lank. Or you might cut it yourself.