wither, droop, lame
凅 centers on loss of vitality: withering, drooping, or becoming lame. The meanings share the idea of something weakening or losing its proper form.
凅 combines 冫 (ice) with 固 (hard, solid), suggesting something frozen solid and thus withered or stiff. The exact historical development is uncertain, but the component combination fits the meaning of loss of vitality through cold or rigidity.
Ice (冫) makes things hard and solid (固), like a plant that freezes and withers, droops, or becomes lame.
For コ, imagine a frozen, withered plant that looks like a small, hard 'co'conut: co -> コ, and the ice has made it solid and lame.