The Koine Greek word, skándalon means either a 'trap-stick' or a 'stumbling block'. In the Bible, skándalon is used figuratively to mean either something that causes people to sin, or something that causes them to lose their faith in Jesus.

1. A trap-stick: a stick holding open a baited trap; when a creature touches it, it releases the trap door to capture the prey. This figuratively refers to a person that entices someone into wrongdoing, getting them to thereby harm or destroy themselves. For example, Peter tempting Christ to refuse the crucifixion. Causing others to sin endangers their connection to God and potentially destroys their souls. If the victim thereby falls into mortal sin, the scandalous deed is considered to be likewise mortal sin.
2. A stumbling stone or tripwire: anything that makes someone trip and fall. This figuratively means "something that causes someone to lose faith in Jesus".