The antonyms for the word in-vulnerable are fragile, vulnerable, weak, defenseless, delicate, exposed, open, and susceptible. These words describe something that is easily harmed, damaged, or influenced by outside forces. Fragile refers to something that is prone to breaking or shattering under pressure. Vulnerable and weak both suggest susceptibility to harm or attack. Defenseless implies a lack of protection or means to defend oneself. Delicate suggests something subtle and easily damaged. Exposed and open both imply a lack of protection or concealment. Susceptible indicates a vulnerability to influence or infection. These antonyms are useful in describing situations where protection or security is lacking.