From Longman Dictionary of Contemporary Englishan eternityan eternityLONG TIMEa period of time that seems very long because you are annoyed, anxious etc 🔊 Here she waited for what seemed like an eternity. 🔊 That week was an eternity of solitude and boredom. →eternity
Examples from the Corpus
an eternity• We only waited five minutes, but it seemed like an eternity.