A giveaway is something that shows or hints at what someone's problem or issue might be.
You often hear about giveaways when it comes to health problems - if there are signs of something going wrong with a person's body, like pain in their joints, they can be a giveaway for arthritis. Doctors and patients alike use giveaways to figure out the cause of symptoms, so treatment can begin. In other situations, a giveaway might be an early warning sign that something is not quite right - maybe your friend has been acting really strange lately and you notice them being really short with people; that could be a giveaway that they're stressed about something.
Something that is given away or handed out for free.
Example: The T-shirt was a giveaway from the company that sells the software.
