very depressed or extremely unhappy and showing an impulse to kill oneself, or broadly relating to, suggesting, or constituting the desire or action of killing oneself;
e.g. A person who is feeling suicidal should seek professional help immediately.
(adjective)
damaging or dangerous to oneself or one's life, destructive or disastrous to one's interests;
e.g. They plan will be suicidal if it fails, so they want to be absolutely sure of its success before putting it into effect.