No longer new or fresh, usually as a result of being kept for too long. (Cambridge Dictionary)
Not fresh and new; boring because too familiar. (Cambridge Dictionary)
Used to describe someone who has lost interest in what they are doing because of being bored or working too hard: (Cambridge Dictionary)
(of food) no longer fresh and pleasant to eat; hard, musty, or dry. (Oxford Dictionaries)
No longer new and interesting or exciting. (Oxford Dictionaries)
Tasteless or unpalatable from age. (Merriam – Webster)
Tedious from familiarity. (Merriam – Webster)
Why does food get stale over time?