something that is given free to a customer

something that tells or shows something secret, often without intending to

He said he'd given up smoking, but the empty packs in the bin were a dead giveaway (= clearly showed the secret truth). 他说他已经戒烟了，但是垃圾桶里的空烟盒让他彻底露了马脚。

A giveaway price is very low.

The furniture shop's offering three-piece suites at giveaway prices. 家具店正以极低廉的价格出售一组三件套家具。