Halcyon days are a time of peace, tranquility, and happiness. Synonyms of halcyon days include the following words: prosperous, blissful, golden, idyllic, joyful, serene, untroubled, tranquil. Prosperous denotes a time of abundance and success, while blissful is used to describe a period of supreme happiness and contentment. Golden suggests a time of great value and cherished memories, while idyllic is used when describing a period of peaceful and carefree living. Joyful implies a time of great merriment and celebration, while serene suggests a peaceful and calm period. Finally, untroubled implies a time of ease and freedom from difficulties and problems.