IPA: /ˈsɛt.bæk/
KK: /ˈsɛtˌbæk/
A problem or difficulty that delays progress or makes things worse.
The project faced a major setback when the funding was cut.
Setback is formed from "set" (from Old English *settan*, meaning to place or put) and "back" (meaning the rear or reverse side). The word describes a situation where progress is hindered or reversed, as if something has been placed back.
Think of something being 'placed back' ('set') to remember that a setback means a reversal in progress.