绑 means to tie up or bind, often securely with rope or string, and can also mean to kidnap. For tying, 拴 is specifically tethering an animal, 扎 is bundling (e.g., hair), and 系 is fastening (e.g., shoelaces). For kidnapping, 拐 implies swindling/deception, 劫持 is hijacking a vehicle, and 绑架 is the full term for kidnap.